This patch contains a fix for the MDEV-17262/17243 issues and
new mtr test.

These issues (MDEV-17262/17243) have two reasons:

1) After an intermediate commit, a transaction loses its status
of "transaction that registered in the MySQL for 2pc coordinator"
(in the InnoDB) due to the fact that since version 10.2 the
write_row() function (which located in the ha_innodb.cc) does
not call trx_register_for_2pc(m_prebuilt->trx) during the processing
of split transactions. It is necessary to restore this call inside
the write_row() when an intermediate commit was made (for a split
transaction).

Similarly, we need to set the flag of the started transaction
(m_prebuilt->sql_stat_start) after intermediate commit.

The table->file->extra(HA_EXTRA_FAKE_START_STMT) called from the
wsrep_load_data_split() function (which located in sql_load.cc)
will also do this, but it will be too late. As a result, the call
to the wsrep_append_keys() function from the InnoDB engine may be
lost or function may be called with invalid transaction identifier.

2) If a transaction with the LOAD DATA statement is divided into
logical mini-transactions (of the 10K rows) and binlog is rotated,
then in rare cases due to the wsrep handler re-registration at the
boundary of the split, the last portion of data may be lost. Since
splitting of the LOAD DATA into mini-transactions is technical,
I believe that we should not allow these mini-transactions to fall
into separate binlogs. Therefore, it is necessary to prohibit the
rotation of binlog in the middle of processing LOAD DATA statement.

https://jira.mariadb.org/browse/MDEV-17262 and
https://jira.mariadb.org/browse/MDEV-17243

In the function make_cond_for_table_from_pred a call of ix_fields()
missed checking of the return code. As a result an extracted constant
condition could be not well formed and this caused an assertion failure.

Includes:

MDEV-17302 Add support for ALTER USER command in prepared statement

and

MDEV-17673 main.cte_recursive fails in bb-10.4-ps branch in --ps

  Set correct SELECT_LEX linkage for recursive CTEs.
  Do not delegate this job to TABLE_LIST::set_as_with_table,
  because it is only run on prepare, while With_element::move_anchors_ahead
  is run both on prepare and execute (fix by Igor)

note: Inherit String from Sql_alloc,
to get operators new and new[] in sync

in rocksdb gcc was complaining that non-lvalue was cast to const.

When there is a huge transaction in the undo log, the purge threads
may get stuck in trx_purge_attach_undo_recs() for a long time,
causing the server to hang on a normal shutdown (innodb_fast_shutdown>0).

Apparently the innodb_purge_batch_size does not work correctly, or the
n_pages_handled is not being incremented correctly. We do not fix that
for now, but we will instead check if shutdown has been initiated,
allowing the purge threads to shut down without delays.

MDEV-16958 Assertion `field_length < 5' failed in Field_year::val_str or data corruption upon SELECT with UNION and aggregate functions

There were two newly enabled warnings:
1. cast for a function pointers. Affected sql_analyse.h, mi_write.c
   and ma_write.cc, mf_iocache-t.cc, mysqlbinlog.cc, encryption.cc, etc

2. memcpy/memset of nontrivial structures. Fixed as:
* the warning disabled for InnoDB
* TABLE, TABLE_SHARE, and TABLE_LIST got a new method reset() which
  does the bzero(), which is safe for these classes, but any other
  bzero() will still cause a warning
* Table_scope_and_contents_source_st uses `TABLE_LIST *` (trivial)
  instead of `SQL_I_List<TABLE_LIST>` (not trivial) so it's safe to
  bzero now.
* added casts in debug_sync.cc and sql_select.cc (for JOIN)
* move assignment method for MDL_request instead of memcpy()
* PARTIAL_INDEX_INTERSECT_INFO::init() instead of bzero()
* remove constructor from READ_RECORD() to make it trivial
* replace some memcpy() with c++ copy assignments

The symptom of the bug was that one got the following in
the aria recovery log:
"Table 'xxx', id 57, has create_rename_lsn (1,0x12dee) more recent than LOGREC_FILE_ID's LSN (1,0x12dc4), ignoring open request"

After this all future redo entries was marked with
"For table of short id 57, table skipped, so skipping record"

Analyze:
When ending batch insert, create_rename_lsn for the table
is updated to signal that earlier redo entries for the
table can't be applied. The problem was that future redo
entries was also ignored as redo code assumed they where
for the old table.

Fixed by calling translog_dessign_id, which causes
future redo entries to be seen as belonging to the
updated table.

On startup, if the InnoDB doublewrite buffer can be used to
recover a corrupted page, raising an ERROR about a recoverable
error seems inappropriate. Issue Note instead, and adjust
tests accordingly.

Also, correctly validate the tablespace ID in the files.

Tests for MDEV-18667 ASAN heap-use-after-free in make_date_time / Arg_comparator::compare_string / Item_func_nullif::compare

The patch for MDEV-14926 fixed MDEV-18667 as well. Adding tests only.

MDEV-14926 AddressSanitizer: heap-use-after-free in make_date_time on weird combination of functions

The native InnoDB partitioning was never enabled in MariaDB.
Remove some declarations and comments referring to it.

row_drop_tables_for_mysql_in_background(): Copy the table name
before closing the table handle, to avoid heap-use-after-free if
another thread succeeds in dropping the table before
row_drop_table_for_mysql_in_background() completes the table name lookup.

dict_mem_create_temporary_tablename(): With innodb_safe_truncate=ON
(the default), generate a simple, unique, collision-free table name
using only the id, no pseudorandom component. This is safe, because
on startup, we will drop any #sql tables that might exist in InnoDB.
This is a backport from 10.3. It should have been backported already
as part of backporting MDEV-14717,MDEV-14585 which were prerequisites
for the MDEV-13564 backup-friendly TRUNCATE TABLE.
This seems to reduce the chance of table creation failures in
ha_innobase::truncate().

ha_innobase::truncate(): Do not invoke close(), but instead
mimic it, so that we can restore to the original table handle
in case opening the truncated copy of the table failed.

If wsrep provider (i.e. galera library) is defined but wsrep_on=OFF
we should not force row binlog row format.

Problem was that we skipped background persistent statistics calculation
on applier nodes if thread is marked as high priority (a.k.a BF).
However, on applier nodes all DDL which is replicate will be executed
as high priority i.e BF.

Fixed by allowing background persistent statistics calculation on
applier nodes even when thread is marked as BF. This could lead
BF lock waits but for queries on that node needs that statistics.

Removed redundant plugin_thdvar_cleanup() from end_connection(): called by
THD::free_connection(), which always follows end_connection().

Saves at least one lock(LOCK_plugin) and one
rdlock(LOCK_system_variables_hash).

Benchmarked on a 2socket/20core/40threads Broadwell system using sysbench
connect brencmark @40 threads (with select 1 disabled).

10.2 shows moderate improvement: 136219.93 -> 137766.31 CPS.
10.3 is improvement is somewhat better: 93018.29 -> 101379.77 CPS.

Also backported MyRocks memory leak fix from 10.4, which turned out to
be unrelated.

We do want to ignore InnoDB's internal #sql-ib*.ibd at shutdown,
because those tables will be dropped on the next startup.
Failure to filter out these table names occasionally causes some
unwanted output for tests that restart InnoDB soon after dropping
or truncating tables, for example innodb.recovery_shutdown.

This also fixes -Wstringop-truncation that GCC 8 issued for strncpy().

The patch for MDEV-15945 fixed MDEV-18892. Adding tests only.

MDEV-18502: Server crash in find_field_in_tables upon 2nd execution of SP which causes ER_WRONG_GROUP_FIELD

Fixed by the commit cb11b3fb.
Adding the test case for this issue.

The issue here was when we had a subquery and a window function in an expression in
the select list then subquery was getting computed after window function computation.
This resulted in incorrect results because the subquery was correlated and the fields
in the subquery was pointing to the base table instead of the temporary table.

The approach to fix this was to have an additional field in the temporary table
for the subquery and to execute the subquery before window function execution.
After execution the values for the subquery were stored in the temporary table
and then when we needed to calcuate the expression, all we do is read the values
from the temporary table for the subquery.

Make mysqltest to use --ps-protocol more

use prepared statements for everything that server supports
with the exception of CALL (for now).

Fix discovered test failures and bugs.

tests:
* PROCESSLIST shows Execute state, not Query
* SHOW STATUS increments status variables more than in text protocol
* multi-statements should be avoided (see tests with a wrong delimiter)
* performance_schema events have different names in --ps-protocol
* --enable_prepare_warnings

mysqltest.cc:
* make sure run_query_stmt() doesn't crash if there's
  no active connection (in wait_until_connected_again.inc)
* prepare all statements that server supports

protocol.h
* Protocol_discard::send_result_set_metadata() should not send
  anything to the client.

sql_acl.cc:
* extract the functionality of getting the user for SHOW GRANTS
  from check_show_access(), so that mysql_test_show_grants() could
  generate the correct column names in the prepare step

sql_class.cc:
* result->prepare() can fail, don't ignore its return value
* use correct number of decimals for EXPLAIN columns

sql_parse.cc:
* discard profiling for SHOW PROFILE. In text protocol it's done in
  prepare_schema_table(), but in --ps it is called on prepare only,
  so nothing was discarding profiling during execute.
* move the permission checking code for SHOW CREATE VIEW to
  mysqld_show_create_get_fields(), so that it would be called during
  prepare step too.
* only set sel_result when it was created here and needs to be
  destroyed in the same block. Avoid destroying lex->result.
* use the correct number of tables in check_show_access(). Saying
  "as many as possible" doesn't work when first_not_own_table isn't
  set yet.

sql_prepare.cc:
* use correct user name for SHOW GRANTS columns
* don't ignore verbose flag for SHOW SLAVE STATUS
* support preparing REVOKE ALL and ROLLBACK TO SAVEPOINT
* don't ignore errors from thd->prepare_explain_fields()
* use select_send result for sending ANALYZE and EXPLAIN, but don't
  overwrite lex->result, because it might be needed to issue execute-time
  errors (select_dumpvar - too many rows)

sql_show.cc:
* check grants for SHOW CREATE VIEW here, not in mysql_execute_command

sql_view.cc:
* use the correct function to check privileges. Old code was doing
  check_access() for thd->security_ctx, which is invoker's sctx,
  not definer's sctx. Hide various view related errors from the invoker.

sql_yacc.yy:
* initialize lex->select_lex for LOAD, otherwise it'll contain garbage
  data that happen to fail tests with views in --ps (but not otherwise).

This solves the following issues:

* unlike lex->m_sql_cmd and lex->sql_command, thd->query_plan_flags
  is not reset in Prepared_statement::execute, it survives
  till the log_slow_statement(), so slow logging behaves correctly in --ps

* using thd->query_plan_flags for both slow_log_filter and
  log_slow_admin_statements means the definition of "admin" statements
  for the slow log is the same no matter how it is filtered out.

Added metadate info after prepare EXPLAIN/ANALYZE.

Prepare os ANALYZE now respond as EXPLAIN.

recv_parse_log_recs(): Do not compare type if ptr==end_ptr
(we have reached the end of the redo log parsing buffer),
because it will not have been correctly initialized in that case.