MDEV-6657: Poor plan choice for ORDER BY key DESC optimization...

The problem was caused by the following scenario:
- range optimizer picks an index IDX1 which doesn't match the ORDER BY ...
  LIMIT clause.
- test_if_skip_sort_order() decides to switch to index IDX2 which matches
  the ORDER BY ... LIMIT.
- it runs SQL_SELECT::test_quick_select() for the second time to produce
  an quick select for IDX2.
- However, test_quick_select() would figure that full index scan on IDX1
  is still cheaper (its calculations ignore the LIMIT n).

Fixed this by
- passing force_quick_range=true to test_quick_select()
- in test_quick_select, don't consider full index scans if the mentioned
  parameter is true.

Numerous changes in .result files are caused by test_quick_select() being
run after "early/late NULLs filtering" feature has injected NOT NULL
condition.
Merge 10.1 into bb-10.1-mdev6657
MDEV-6402: Optimizer doesn't choose best execution plan when composite...

Fix test_if_skip_sort_order() logic:
WHEN
we use index X, which doesn't produce needed ordering, but there is
an index Y which does and has the same prefix as used prefix of X
THEN
don't just switch to using ref access on Y. If range(Y) would use more
key parts, use range(Y).
Merge ../10.1-mdev6402 into bb-10.1-orderby-fixes
Merge ../10.1-mdev6657 into bb-10.1-orderby-fixes
MDEV-6796: Unable to skip filesort when using implicit extended key

Re-work test_if_order_by_key() to work correctly for extended indexes.
MDEV-6814: Server crashes in calculate_key_len on query with ORDER BY
- if test_if_skip_sort_order() decides to switch to using an index, or
  switch from using ref to using quick select, it should set all
  members accordingly.
Minor modifications

- Simplified test cases in wsrep.variables
- Fixed a condition in wsrep_check_opts.cc
- Fixed an "unbound variable" in wsrep_sst_rsync
MDEV-6833: SIGSEGV on shutdown with non-default wsrep_slave_threads

thd->variables' table_plugin & tmp_table_plugin should be set to
NULL for wsrep system threads.
Also made a minor change to skip checking of wsrep options if
wsrep_on is not set.
Merge ../10.1-orderby-fixes into 10.1
MDEV-6667: Merged fix from maria-10.0-galera.
MDEV 4427: query timeouts

Added MAX_STATEMENT_TIME user variable to automaticly kill queries after a given time limit has expired.

- Added timer functions based on pthread_cond_timedwait
- Added kill_handlerton() to signal storage engines about kill/timeout
- Added support for GRANT ... MAX_STATEMENT_TIME=#
- Copy max_statement_time to current user, if stored in mysql.user
- Added status variable max_statement_time_exceeded
- Added KILL_TIMEOUT
- Removed digest hash from performance schema tests as they change all the time.
- Updated test results that changed because of the new user variables or new fields in mysql.user

This functionallity is inspired by work done by Davi Arnaut at twitter.
Test case is copied from Davi's work.

Documentation can be found at
https://kb.askmonty.org/en/how-to-limittimeout-queries/

mysql-test/r/mysqld--help.result:
  Updated for new help message
mysql-test/suite/perfschema/r/all_instances.result:
  Added new mutex
mysql-test/suite/sys_vars/r/max_statement_time_basic.result:
  Added testing of max_statement_time
mysql-test/suite/sys_vars/t/max_statement_time_basic.test:
  Added testing of max_statement_time
mysql-test/t/max_statement_time.test:
  Added testing of max_statement_time
mysys/CMakeLists.txt:
  Added thr_timer
mysys/my_init.c:
mysys/mysys_priv.h:
  Added new mutex and condition variables
  Added new mutex and condition variables
mysys/thr_timer.c:
  Added timer functions based on pthread_cond_timedwait()
  This can be compiled with HAVE_TIMER_CREATE to benchmark agains timer_create()/timer_settime()
sql/lex.h:
  Added MAX_STATEMENT_TIME
sql/log_event.cc:
  Safety fix (timeout should be threated as an interrupted query)
sql/mysqld.cc:
  Added support for timers
  Added status variable max_statement_time_exceeded
sql/share/errmsg-utf8.txt:
  Added ER_QUERY_TIMEOUT
sql/signal_handler.cc:
  Added support for KILL_TIMEOUT
sql/sql_acl.cc:
  Added support for GRANT ... MAX_STATEMENT_TIME=#
  Copy max_statement_time to current user
sql/sql_class.cc:
  Added timer functionality to THD.
  Added thd_kill_timeout()
sql/sql_class.h:
  Added timer functionality to THD.
  Added KILL_TIMEOUT
  Added max_statement_time variable in similar manner as long_query_time was done.
sql/sql_connect.cc:
  Added handling of max_statement_time_exceeded
sql/sql_parse.cc:
  Added starting and stopping timers for queries.
sql/sql_show.cc:
  Added max_statement_time_exceeded for user/connects status in MariaDB 10.0
sql/sql_yacc.yy:
  Added support for GRANT ... MAX_STATEMENT_TIME=# syntax, to be enabled in 10.0
sql/structs.h:
  Added max_statement_time user resource
sql/sys_vars.cc:
  Added max_statement_time variables
mysql-test/suite/roles/create_and_drop_role_invalid_user_table.test
  Removed test as we require all fields in mysql.user table.
scripts/mysql_system_tables.sql
scripts/mysql_system_tables_data.sql
scripts/mysql_system_tables_fix.sql
  Updated mysql.user with new max_statement_time field
Removed files that had been accidentally committed
Removed compiler warnings
Merge branch '10.1' of github.com:MariaDB/server into 10.1

Merge with main branch
followup changes to timeout commit

* fix debian patch
* update the copyright
* rename include guards to follow conventions
* restore incorectly deleted test file, add clarification in a comment
* capitalize the first letter of the status variable
cleanup: simplify the usage of WSREP_FORMAT macro
MDEV-5749 Please add a .pc file to MariaDB for easy use via pkg-config
cleanup: galera misc cleanups

also disable galera-specific output in mysql_tzinfo_to_sql,
it'll be enabled later.
Plugin API: increase SHOW_VAR_FUNC_BUFF_SIZE for 64-bit CPUs

instead of having it 1K everywhere, make it 1K on 32-bit and 2K on 64-bit.
As the latter has larger pointers (and larger sizeof(SHOW_VAR),
it needs a larger buffer to store the same amount of SHOW_VARs
cleanup: case SQLCOM_CALL

move SP invocation code out of the huge switch in mysql_execute_command