fix a bad merge

Problem was NULL-pointer reference. Fixed by removing unnecessary and not
really working recursive reserver thread lookup.

and a couple of collaterals:
* debugging assert in my_valgrind.h
* trivial cleanup in sql_union.cc

fix a race condition in the test

In some cases the function compare_order_elements() erroneously
returned CMP_EQ for not equal elements.

Updated mysqld--help,win.rdiff.

Some compilers are unhappy about mixed struct/class declarations.

Fixed type cast.

Fixed sysvars_server_[not]embedded failure: changed type of
table_open_cache_instances from ulong to uint.

Added casts foratomic operations around tc_active_instances and
tc_contention_warning_reported: needed on some platforms.

Table cache instances autosizing.

Improve scalability by implementing multi-instance table cache.

because InnoDB 5.7 tdecided to store a full path there

test. We should not take X-lock for index in the begining, setting
tablespace as named space is enough.

add_identifier change comes from 5.7, everything else is a follow-up

* update (some) tests from 5.7
* update results (e.g. cardinality is no longer reported)
* uncomment MYSQL_PLUGIN_FULLTEXT_PARSER/MYSQL_FTS_PARSER code
* initialize m_prebuilt->m_fts_limit manually,
   as we do not use ft_init_ext_with_hints()

We need to pass nonatomic=false (dont allow data dict unlock),
because the transaction may hold locks on SYS_* tables from
previous calls to fts_drop_table().

innodb-strict-mode by default is now ON, disabling it for
this test because test uses INDEX DICECTORY that is not
really supported by InnoDB.

Fixed auto_increment_dup test. Current behavior is correct for repeatable read (and
serializable) isolation levels. Old behavior is correct for read committed
isolation level.

The condition pushed into WHERE/HAVING of a materialized
view/derived table may differ for different executions of
the same prepared statement. That's why the should be
ANDed with the existing WHERE/HAVING conditions only after all
permanent transformations of these conditions has been
performed.

information_schema.innodb_changed_pages IS table available only on
xtradb, add possible error for now.

Do not push conditions into materialized views/derived tables
marked with the flag 'fill_me'.

Don't wait until os_thread_exit to close it.
Remove code from innodb_shutdown to close handles on Windows.

crash

MDEV-10779 Failing assertion lex->proc_list.elements == 0 or syntax error on PROCEDURE ANALYSE in UNION

Reverting a part of the patch for "MDEV-8909union parser cleanup",
as a parenthesized SELECT with PROCEDURE followed by UNION is not
disallowed by the grammar (only a non-parenthesized SELECT with PROCEDURE
followed by a UNION is disallowed grammatically).

When running with --ps protocol, window functions cleanup method may
be called twice. Enforce proper cleanup by setting pointers to NULL
after deletion. This prevents double deletion on second cleanup.