Analysis: Flush changed page bitmaps calls log_online_follow_redo_log
that later calls log_group_read_log_seg with release_mutex = true
and that causes the log_sys mutex being released before
log_decrypt_after_read function that later required log_sys mutex.

Fix: Enter log_sys mutex before log_decrypt_after_read if mutex
is released and release the mutex after the function if we
acquired it before function call.

Time column of SHOW PROCESSLIST was returned in microseconds after rev. 8f603bcb.
Revert original timescale (seconds).

TDC_element::free_tables_back() had pre-lfhash leftover code, which referenced
TDC_element::free_tables via TDC_element::share. This is not correct as share
may be NULL (newly inserted or to be removed), instead access free_tables
directly.

ORDER BY against union may confuse name resolution context, causing valid
SQL statements to fail.

The purpose of context change was presumably intended for the duration of
gathering field list for ORDER BY. However it isn't actually required (name
resolution context is never accessed by the latter).

See also alternative solution (in MySQL 5.7): 92145b95.

Test create_or_replace should make sure that background decrypt
operation is finished and flush all dirty pages using restart
to clean up the database before ending.

It's now needed outside of Item_bool_func2 any more.

fix two #if MYSQL_VERSION_ID > 100105

SEQ_READ_APPEND is for two threads (reader and writer)
simultaneously accessing the IO_CACHE

Pretend that CREATE TABLE and CREATE TEMPORARY TABLE are
two different commands internally. The user doesn't need
to know that they both are SQLCOM_CREATE_TABLE.

Same for DROP [TEMPORARY] TABLE

* keep all com_xxx constants together in struct system_status_var
* fix an outdated comment in sql_cmd.h
* fix an off-by-one bug in mysqld.cc

as a bonus that makes CREATE TEMPORARY TEMPORARY TABLE illegal

Old code worked because plugin locking guaranteed that
encryption plugin is deinitialized last.
But compiled-in plugins are never locked.

This fixes encryption failures on fulltest builder

* support statically compiled file_key_management when possible
* rename encryption.encryption_create_or_replace -> encryption.create_or_replace
* delete unnecessary *.opt file (including
  have_key_management_plugin.inc is enough)
* remove unnecessary LOWER() for strings that are compared
  case insensitively anyway

Disable sys_vars.all_vars test. There's no need to write
boilerplate tests for every new system variable, our
INFORMATION_SCHEMA.SYSTEM_VARIABLES and sysvar_* tests
are now used to show all basic properties of all variables.

fix aes_decrypt of yassl to support zero-length input

Moving Item_func_spatial_rel from Item_bool_func to Item_bool_func2.
to make OP(const,field) use indexes.
- MBR functions supported OP(const,field) optimization in 10.0,
but were inintentionally broken in an earlier 10.1 change that introduced
a common parent for Item_func_spatial_mbr_rel and Item_func_spatial_precise_rel.
- Precise functions never supported optimization for OP(const,field).
Now both MBR and precise functions support OP(const,field) optimization.

any of the optimizer related functionality.

count_sargable_conds() instead for Item_func_in, Item_func_null_predicate,
Item_bool_func2. There other Item_int_func descendants that used to set
"sargable" to true (Item_func_between, Item_equal) already have their
own implementation of count_sargable_conds(). There is no sense to
have two parallel coding models for the same thing.

adding a separte class Item_func_spatial_relate for ST_RELATE().
This is a preparatory patch for:
 MDEV-8239 Reverse spatial operations OP(const, field) do not get optimized

Change session only variable enforce_storage_engine to be
session variable and make sure that also global value
is used if session variable is not set.

Item_func_eq's created during conversion of a ROW equality to a conjunction
of scalar equalities did not set cmp_context for its arguments properly,
so some of these created Item_func_eq could be later erroneously eliminated.

MDEV-8373 Zero date can be inserted in strict no-zero mode through CREATE TABLE AS SELECT timestamp_field

don't return NULL-s anymore, and actually they're not BOOLEAN.
Fixed.