- Call delete_statistics_tables() after lock_table_names in drop tables.
  This avoids a deadlock issue with FTWRL and future backup locks.
- Added some missing clear_error()
- Ensure we don't clear error caused by the caller
- Updated function comments

- Re-numbered enum_table_category to make some tests easier
- Moved TABLE_CATEGORY_INFORMATION to be first CATEGORY of virtual tables
- Don't take MDL locks for not updateable table category's

Part of MDEV-5336 Implement LOCK FOR BACKUP

FLUSH TABLE table_names have changed slighty as we are now opening
tables before taking the MDL lock. The difference is that FLUSH TABLE
table_name will now be blocked by a table that is waiting for FTWRL.
There should not be any new deadlocks as part of this change.

The end result is still better in most cases as FTWRL is now only
waiting for write statements to end, not for read only statements and
it's not flushing tables in use from the table cache.

Share will be needed to be able to determine if table supports online
backup. Appropriate metadata lock type in BACKUP namespace will be
acquired basing on this information.

Also made pending global read lock request to be preferred victim of MDL
deadlock detector. This allows us to hide some non-fatal deadlocks and
make FTWRL less likely to break concurrent queries.

Part of MDEV-5336 Implement LOCK FOR BACKUP

Other things:
- Added printing of MDL locks to DBUG.

Part of MDEV-5336 Implement LOCK FOR BACKUP

Originally both table metadata lock and global read lock protection
were acquired before getting TABLE from table cache. This will be
reordered in a future commit with MDL_BACKUP_XXX locks so that we
first take table metadata lock, then get TABLE from table cache, then
acquire analogue of global read lock.

This patch both simplifies FLUSH TABLES code, makes FLUSH TABLES to
lock less and also enables FLUSH TABLES code to be used with backup
locks.

The usage of FLUSH TABLES changes slightly:
- FLUSH TABLES without any arguments will now only close not used tables
  and tables locked by the FLUSH TABLES connection.  All not used table
  shares will be closed.
  Tables locked by the FLUSH TABLES connection will be reopened and
  re-locked after all others has stoped using the table (as before).
  If there was no locked tables, then FLUSH TABLES is instant and will
  not cause any waits.
  FLUSH TABLES will not wait for any in use table.
- FLUSH TABLES with a table list, will ensure that the tables are closed
  before statement returns. The code is now only using MDL locks and not
  table share versions, which simplices the code greatly. One visible
  change is that the server will wait for the end of the transaction that
  are using the tables. Before FLUSH TABLES only waited for the statements
  to end.
Signed-off-by: Monty <monty@mariadb.org>

FLUSH TABLES kills all insert delayed treads. If this happens at same time
as a newly started insert delayed query, the insert may fail with either
and error ("Query interrupted") or the row may be lost.
This patch fixes this by changing a failed attempt of get_delay_table() to
convert the query to use a normal insert.

The test case for this patch can be found in the FLUSH TABLES commit after
this one.

Part of MDEV-5336 Implement LOCK FOR BACKUP

The idea is that instead of waiting in close_cached_tables() for all
tables to be closed, we instead call flush_tables() that does:
- Flush not used objects in table cache to free memory
- Collect all tables that are open
- Call HA_EXTRA_FLUSH on the objects, to get them into "closed state"
- Added HA_EXTRA_FLUSH support to archive and CSV
- Added multi-user protection to HA_EXTRA_FLUSH in MyISAM and Aria

The benefit compared to old code is:
- FTWRL doesn't have to wait for long running read operations or
  open HANDLER's

Part of MDEV-5336 Implement LOCK FOR BACKUP

Added support for backup calls in Aria to protect
removal of redo logs.

- The old code used the original create_info from lex, not the new one
  that includes more information (like OPT_OR_REPLACE).
  The bug was not discovered as the code in lock_table_named() only
  checked for OPT_OR_REPLACE in case of timeout errors.
  As lock_table_names will be fixed as part of BACKUP STAGE's, there
  is no changes in lock_table_names() in this commit.
- Removed also the 'temporary' copy of statement flags to thd for
  lock_table_names()

- Moved tests depending on utf8 characters from create to create_utf8
- Fixed some tests in create and sp that wrongly tried to create table
  from non existing table on existing table.  In a later patch we may
  first check if table exists, in which case the error message would
  change.
- Updated results for partition_debug_tokudb

Bascially this means that all builds with BUILD scripts are done with
--with-jemalloc=NO      # Required by tokudb
--with-ssl              # Required on OpenSuse 10.5 to get galera to work

- Remove obsolete documentation files
- Removed old obsolete information from some documentation files

Added to new values to the server variable use_stat_tables.
The values are COMPLEMENTARY_FOR_QUERIES and PREFERABLY_FOR_QUERIES.
Both these values don't allow to collect EITS for queries like
    analyze table t1;
To collect EITS we would need to use the syntax with persistent like
   analyze table t1 persistent for columns (col1,col2...) index (idx1, idx2...) / ALL

Changing the default value from NEVER to PREFERABLY_FOR_QUERIES.

use_stat_tables= PREFERABLY
optimizer_use_condition_selectivity= 4

MDEV-17928 Conversion from TIMESTAMP to VARCHAR SP variables does not work well on fractional digits

Sort acl_users inside the mysql_rename_user()'s loop, after every
successful iteration.

This is needed because on the next loop's iteration find_user_exact()
is used, which requires correct sorting by name.

&sys_buf + DATA_TRX_ID_LEN is not &(sys_buf + DATA_TRX_ID_LEN).

create_table_def(), ha_innobase::create(): Defer fts_optimize_add_table()
until after the table has been successfully created.

row_fts_merge_insert(): Correctly initialize DB_ROLL_PTR to a safe value
that will not be dereferenced by MVCC.

This patch changes how old rows in mysql.gtid_slave_pos* tables are deleted.
Instead of doing it as part of every replicated transaction in
record_gtid(), it is done periodically (every @@gtid_cleanup_batch_size
transaction) in the slave background thread.

This removes the deletion step from the replication process in SQL or worker
threads, which could speed up replication with many small transactions. It
also decreases contention on the global mutex LOCK_slave_state. And it
simplifies the logic, eg. when a replicated transaction fails after having
deleted old rows.

With this patch, the deletion of old GTID rows happens asynchroneously and
slightly non-deterministic. Thus the number of old rows in
mysql.gtid_slave_pos can temporarily exceed @@gtid_cleanup_batch_size. But
all old rows will be deleted eventually after sufficiently many new GTIDs
have been replicated.