Synchronizing sources in:
- my_wildcmp_uca_impl() handling utf8_unicode_ci
- my_wildcmp_unicode_impl() handling utf8_general_ci

The latter has already had a fix for a similar MySQL bug in utf8_general_ci:
Bug#11754 SET NAMES utf8 followed by SELECT "A\\" LIKE "A\\" returns 0
So fix is now propagated to utf8_unicode_ci.

These bugs:
MDEV-13119 Wrong results with CAST(AS CHAR) and subquery
MDEV-13120 Wrong results with MAKE_SET() and subquery
were previously fixed by:
MDEV-13790 UNHEX() of a somewhat complicated CONCAT() returns NULL

Adding tests only

Changing the pause from 5 to 10 seconds.

Tests fail due to MDEV-17145

forceful connection close.

Fix is to ensure that when close_connection() is called from shutdown
thread, current_thd is set. This that allocation callback for THD specific
memory won't assert(in debug version), or crash (in 10.1 and later)

close_connection() allocates THD specific memory e.g when it writes
the final error packet, and compression is ON for the connection.

           derived table / view by equality

Now rows of a materialized derived table are always put into a
temporary table before join operation. If BNLH is used to join this
table with the result of a partial join then both operands of the
join are actually put into main memory. In most cases this is not
efficient.
We could avoid this by sending the rows of the derived table directly
to the join operation. However this kind of data flow is not supported
yet.
Fixed by not allowing usage of hash join algorithm to join a materialized
derived table if it's joined by an equality predicate of the form
f=e where f is a field of the derived table.

to guarantee that it's destroyed when plugin deinit is called, not after

Unary minus operation for the smallest possible signed long long value
(LONLONG_MIN) is undefined in C++. Because of this, func_time.test
failed on ppc64 buildbot machines.

Fixing the code to avod using undefined operations.

This is fix is similar to "MDEV-7973 bigint fail with gcc 5.0"

alloc_root(): unpoison only requested amount of bytes instead of a
possible bigger aligned-sized buffer.

For the original test in 10.0 it was not really important if
find_user_wild() or find_user_exact() is used in sp_grant_privileges().
sp-security.test passed with either of them.

Fixing the test so it reliably fails with find_user_wild()
and pass with find_user_exact().

             table->pos_in_locked_tables->table == table'
             failed in mark_used_tables_as_free_for_reuse

Assertion failure can be triggered by some DDL executed under LOCK TABLES
that holds lock for DDL target table multiple times (either explicitly or
implcitly).

When closing all table instances for given table (e.g. when preparing for
table removal during CREATE OR REPLACE), only one instance was removed
from m_locked_tables list.

Later we attempt to re-insert one of the instances in mysql_create_table()/
add_back_last_deleted_lock(), which wasn't actually removed. This leads
to m_locks_tables corruption, specifically loss of all following elements.

Then UNLOCK TABLE won't reset some table instances properly (specifically
pos_in_locked_tables), since they're not present in m_locked_tables.

Eventually such table instance gets released to table cache and then
re-used by subsequent statement, which triggers this assertion failure.

multi_delete sets TABLE::no_cache=1 and should set it to 0 when DELETE is done.

don't create static objects that destroy mutexes from destructors,
and don't destroy mutexes from .so destructor (on-unload) function.

if it happens after exit(), P_S will be long gone by that time

this fixes tokudb tests crashing on quantal-amd64

MDEV-16465 Invalid (old?) table or database name or hang in ha_innobase::delete_table and log semaphore wait upon concurrent DDL with foreign keys

lowercase db and table names before prelocking.

Post-fix for 9180e866

This fixes failures on main.lowercase_table4 on Windows

           for blob column

Moved delete_stat_values_for_table_share() call to proper place.

MDEV-16465 Invalid (old?) table or database name or hang in ha_innobase::delete_table and log semaphore wait upon concurrent DDL with foreign keys

Disable "Invalid (old?) table or database name" warning when
converting table names in InnoDB's get_foreign_key_info().

Because a name can be a temporary table name during the ALTER TABLE,
and some other thread can do SHOW CREATE TABLE for the other table
in the FK relationships _anytime_.

MDEV-16465 Invalid (old?) table or database name or hang in ha_innobase::delete_table and log semaphore wait upon concurrent DDL with foreign keys

ALTER TABLE locks the table with TL_READ_NO_INSERT, to prevent the
source table modifications while it's being copied. But there's an
indirect way of modifying a table, via cascade FK actions.

After previous commits, an attempt to modify an FK parent table
will cause FK children to be prelocked, so the table-being-altered
cannot be modified by a cascade FK action, because ALTER holds a
lock and prelocking will wait.

But if a new FK is being added by this very ALTER, then the target
table is not locked yet (it's a temporary table). So, we have to
lock FK parents explicitly.

Backport of 794f71cb

table_already_fk_prelocked() was looking for a table in the wrong
list (not the complete list of prelocked tables, but only in its tail,
starting from the current table - which is always empty for the last
added table), so for circular FKs it kept adding same tables to the list
indefinitely.

Backport of d6d7e169

Backport of f1362910

Use TABLE::init_one_table(), don't duplicate it.
Put additional initializations into TABLE::init_one_table_for_prelocking()

Backport of f1362910

instead of returning strings for CASCADE/RESTRICT
from every storage engine, use enum values

Backport of a3614d33

test case