This is done to get more free flag bits for alter_info->flags

Renamed all ALTER PARTITION defines to start with ALTER_PARTITION_
Renamed ALTER_PARTITION to ALTER_PARTITION_INFO
Renamed ALTER_TABLE_REORG to ALTER_PARTITION_TABLE_REORG

Other things:
- Shifted some ALTER_xxx defines to get empty bits at end

Main reason was to make it easier to print the above structures in
a debugger. Additional benefits is that I was able to use same
defines for both structures, which simplifes some code.

Most of the code is just removing Alter_info:: and Alter_inplace_info::
from alter table flags.

Following renames was done:
HA_ALTER_FLAGS        -> alter_table_operations
CHANGE_CREATE_OPTION  -> ALTER_CHANGE_CREATE_OPTION
Alter_info::ADD_INDEX -> ALTER_ADD_INDEX
DROP_INDEX            -> ALTER_DROP_INDEX
ADD_UNIQUE_INDEX      -> ALTER_ADD_UNIQUE_INDEX
DROP_UNIQUE_INDEx     -> ALTER_DROP_UNIQUE_INDEX
ADD_PK_INDEX          -> ALTER_ADD_PK_INDEX
DROP_PK_INDEX         -> ALTER_DROP_PK_INDEX
Alter_info:ALTER_ADD_COLUMN    -> ALTER_PARSE_ADD_COLUMN
Alter_info:ALTER_DROP_COLUMN   -> ALTER_PARSE_DROP_COLUMN
Alter_inplace_info::ADD_INDEX  -> ALTER_ADD_NON_UNIQUE_NON_PRIM_INDEX
Alter_inplace_info::DROP_INDEX -> ALTER_DROP_NON_UNIQUE_NON_PRIM_INDEX

Other things:
- Added typedef alter_table_operatons for alter table flags
- DROP CHECK CONSTRAINT can now be done online
- Added checks for Aria tables in alter_table_online.test
- alter_table_flags now takes an ulonglong as argument.
- Don't support online operations if checksum option is used.
- sql_lex.cc doesn't add ALTER_ADD_INDEX if index is not created

fill_alter_table() always thought that index was changed because of
of a wrong check of block_size. Some engines had code to correct this
that should not be needed, Aria didn't and because of this some online
operations didn't work.

This code fixes the comparision of block_size to only compare if it's set.

we have two the same 'if' clauses that check opt_bin_log argument
in mysqld.cc and both clauses go successively one after another.
Let's merge them into one

which says:

    We need the up-cast here, since my_decimal has sign() member functions,
    which conflicts with decimal_t::size

But decimal_t does not provide `size` field.

fts_cmp_set_sync_doc_id(), fts_load_stopword(): Start the transaction
in read-only mode if innodb_read_only is set.

fts_update_sync_doc_id(), fts_commit_table(), fts_sync(),
fts_optimize_table(): Return DB_READ_ONLY if innodb_read_only is set.

fts_doc_fetch_by_doc_id(), fts_table_fetch_doc_ids():
Remove the code to start an internal transaction or to roll back,
because this is a read-only operation.

Fixes MDEV-14761 "Assertion `!mysql_parse_status || thd->is_error() ||
thd->get_internal_handler()' failed in parse_sql"

The session object is not really needed for anything.
We can directly create and free the dummy purge_sys->query->trx.

If CREATE TABLE...FULLTEXT INDEX was initiated right before shutdown,
then the function fts_load_stopword() could commit modifications
after shutdown was initiated, causing an assertion failure in
the function trx_purge_add_update_undo_to_history().

Mark as internal all the read/write transactions that
modify fulltext indexes, so that they will be ignored by
the assertion that guards against transaction commits
after shutdown has been initiated.

fts_optimize_free(): Invoke trx_commit_for_mysql() just in case,
because in fts_optimize_create() we started the transaction as
internal, and fts_free_for_backgruond() would assert that the
flag is clear. Transaction commit would clear the flag.

MDEV-14648 Restore fix for MySQL BUG#39053 - UNINSTALL PLUGIN does not allow the storage engine to cleanup open connections

Also, allow the MariaDB 10.2 server to link InnoDB dynamically
against ha_innodb.so (which is what mysql-test-run.pl expects
to exist, instead of the default name ha_innobase.so).

wsrep_load_data_split(): Instead of referring to innodb_hton_ptr,
check the handlerton::db_type. This was recently broken by me in
MDEV-11415.

innodb_lock_schedule_algorithm: Define as a weak global symbol,
so that WITH_WSREP will not depend on InnoDB being linked statically.
I tested this manually. Notably, running a test that only does
	SET GLOBAL wsrep_on=1;
with a static or dynamic InnoDB and
	./mtr --mysqld=--loose-innodb-lock-schedule-algorithm=fcfs
will crash with SIGSEGV at shutdown. With the default VATS
combination the wsrep_on is properly refused for both the
static and dynamic InnoDB.

ha_close_connection(): Do invoke the method also for plugins
for which UNINSTALL PLUGIN was deferred due to open connections.
Thanks to @svoj for pointing this out.

thd_to_trx(): Return a pointer, not a reference to a pointer.

check_trx_exists(): Invoke thd_set_ha_data() for assigning a transaction.

log_write_checkpoint_info(): Remove an unused DEBUG_SYNC point
that would cause an assertion failure on shutdown after deferred
UNINSTALL PLUGIN.

This was tested as follows:

cmake -DWITH_WSREP=1 -DPLUGIN_INNOBASE:STRING=DYNAMIC \
-DWITH_MARIABACKUP:BOOL=OFF ...
make
cd mysql-test
./mtr innodb.innodb_uninstall

There were two problems related to the bug report:
1. Item_datetime::get_date() was not implemented.
   So execution went through val_int() followed
   by int-to-datetime or int-to-time conversion.
   This was the reason why the optimizer did not
   work well on data with fractional seconds.
2. Item_datetime::set() did not have a TIME specific code
   to mix months and days to hours after unpack_time().
   This is why the optimizer did not work well with negative
   TIME values, as well as huge time values.

Changes:

1. Overriding Item_datetime::get_date(), to return ltime.
   This fixes the problem N1.
2. Cleanup: Moving pack_time() and unpack_time() from
   sql-common/my_time.c and include/my_time.h to
   sql/sql_time.cc and sql/sql_time.h, as they are not needed
   on the client side.
3. Adding a new "enum_mysql_timestamp_type ts_type" parameter
   to unpack_time() and moving the TIME specific code to mix
   months and days with hours inside unpack_time().
   Adding a new "ts_type" parameter to Item_datetime::set(),
   to pass it from the caller down to unpack_time().
   So now the TIME specific code is automatically called
   from Item_datetime::set(). This fixes the problem N2.
   This change also helped to get rid of duplicate TIME specific code
   from other three places, where mixing month/days to hours
   was done immediately after unpack_time().
   Moving the DATE specific code to zero hhmmssff
   from Item_func_min_max::get_date_native to inside unpack_time(),
   for symmetry.
4. Removing the virtual method in_vector::result_type(),
   adding in_vector::type_handler() instead.
   This helps to get result_type(), field_type(),
   mysql_timestamp_type() of an in_vector easier.
   Passing type_handler()->mysql_timestamp_type() as
   a new parameter to Item_datetime::set() inside
   in_temporal::value_to_item().
5. Cleaup: Removing separate implementations of in_datetime::get_value()
   and in_time::get_value(). Adding a single implementation
   in_temporal::get_value() instead.
   Passing type_handler()->field_type() to get_value_internal().

This is regression after bc7a1dc1 of
MDEV-15104 - Optimise MVCC snapshot.

Aforementioned revision removes mutex lock around ReadView creation,
which allows views to be created concurrently. Effectively it
invalidates "oldest view" approach: no single view can be considered
oldest anymore. Instead we have to iterate trx_sys.m_views to find
min(m_low_limit_no), min(m_low_limit_id) and all transaction ids below
min(m_low_limit_id), which would form oldest view.

Second regression comes from c0d5d7c0
of MDEV-15104 - Optimise MVCC snapshot.

It removes mutex protection around trx->no assignment, which opens up
a gap between m_max_trx_id increment and transaction serialisation
number becoming visible through rw_trx_hash. While we're in this gap
concurrent thread may come and do MVCC snapshot without seeing allocated
but not yet assigned serialisation number. Then at some point purge
thread may clone this view. As a result it won't see newly allocated
serialisation number and may remove "unnecessary" history data of this
transaction from rollback segments.

MDEV-13732 User with SELECT privilege can ALTER sequence

GAL-506 breaks galera_defaults MTR test by upping repl.proto_max again. Fix this once and for all by overwriting it with constant string since it makes little sense to check for it in this test.

MDEV-15215 main.partition_explicit_prune fails in bulidbot with assertion failures and server crashes.

        ha_partition::get_open_file_sample() implemented to be used
        when we need a file sample that is surely opened.

lock_trx_release_locks(): Relax a debug assertion to allow
recovered TRX_STATE_COMMITTED_IN_MEMORY transactions.

trx_commit_in_memory(): Add DEBUG_SYNC instrumentation.

trx_undo_insert_cleanup(): Skip persistent changes if innodb_read_only
is set. This should only happen when a recovered committed transaction
would be cleaned up at shutdown.

The patch for MDEV-15287 made the code in Item_func_min_max::get_date_native()
dead, as the TIME data type is now handled in get_time_native().
Removing the TIME related code from get_date_native().

MDEV-14990 mysql_upgrade fails with ERROR 1408 (HY000) at line 566: Event Scheduler: An error occurred when initializing system tables

Don't check mysql.db and mysql.user from event schedule on startup.

Event schedule should only check its own mysql.event table, it has
no business checking other system tables. In particular, it's ridiculous
for event schedule to fail when privilege tables are not the newest,
because sql_acl.cc supports old privilege tables just fine.

Truncate_versioning_priv->Delete_history_priv

because the command and the privilege were renamed

don't expand AS OF in views, and, in particular, don't auto-add
AS OF NOW().

Hide INVISIBLE_SYSTEM columns from writes and from fix_vcol_expr().