- Turning get_mm_tree_for_const() from a static function into
  a protected method in Item.
- Adding a new class Item_bool_func2_with_rev, for the functions and operators
  that have a reverse function and can use the range optimizer for
  to optimize "value OP field" as "field REV_OP value". Deriving
  Item_bool_rowready_func2 and Item_funt_spatial_rel from the new class.
- Removing Item_bool_func2::have_rev_func().

- Item_bool_func::get_func_mm_tree()
- Item_bool_func::get_mm_parts()
- Item_bool_func::get_ne_mm_tree()

from Item_bool_func::get_mm_leaf() into Field_xxx::can_optimize_range().
This reduces the total amount of virtual calls. Also, it's a prerequisite
change for the pluggable data types.

MDEV-8523: InnoDB: Assertion failure in file buf0buf.cc line 5963 (Failing assertion: key_version == 0 || key_version >= bpage->key_version)

Item_ref::val_bool_result().

Check if the engine is supported/allowed before replicating the
statement.

Fixed race condition in code filling INFORMATION_SCHEMA.PROCESSLIST.INFO_BINARY.
When loading query string/length of another connection one must have
LOCK_thd_data locked.

The patch for MDEV-8871 also fixed the problem reported in MDEV-657.
Adding the test case from the bug report.

MDEV-8873 Wrong field type or metadata for LEAST(int_column,string_column)

Analysis: When a page is read from encrypted table and page can't be
decrypted because of bad key (or incorrect encryption algorithm or
method) page was incorrectly left on buffer pool.

Fix: Remove page from buffer pool and from pending IO.

MDEV-8875 Wrong metadata for MAX(CAST(time_column AS DATETIME))

Item_func_hybrid_field_type did not return correct field_type(), cmp_type()
and result_type() in some cases, because cached_result_type and
cached_field_type were set in independent pieces of the code and
did not properly match to each other.
Fix:
- Removing Item_func_hybrid_result_type
- Deriving Item_func_hybrid_field_type directly from Item_func
- Introducing a new class Type_handler which guarantees that
  field_type(), cmp_type() and result_type() are always properly synchronized
  and using the new class in Item_func_hybrid_field_type.

Added error handling to crash recovery so that we stop instead of
asserting.

Alloc creating crypt_data to empty page at crash recovery and redo.

MDEV-8852 Implicit or explicit CAST from MAX(string) to INT,DOUBLE,DECIMAL does not produce warnings

Added per-table boolean IETF_QUOTES variable to CSV storage engine. It allows to
enable IETF-compatible parsing of embedded quote and comma characters. Disabled
by default.

This patch is based on Percona revision:
https://github.com/percona/percona-server/commit/b32fbf02766f8db00f9ff4e6dc05a1df97c10ff7

Note that original patch adds server variable, while this patch adds per-table
variable.

Addendum:
* Before calling THD::init_for_queries(), flip the current_thd to wsrep
thread so that memory gets allocated for the right THD.
* Use wsrep_creating_startup_threads instead of plugins_are_initialized
as the condition for the execution of THD::init_for_queries() within
start_wsrep_THD(), as use of latter could still leave some room for
race.

Problem:
When mysqld starts as a galera node, it creates 2 system threads
(applier & rollbacker) using start_wsrep_THD(). These threads are
created before plugin initialization (plugin_init()) for SST methods
like rsync and xtrabackup.

The threads' initialization itself can proceed in parallel to mysqld's
main thread of execution. As a result, the thread initialization code
(start_wsrep_THD()) can end up accessing some un/partially initialized
structures (like maria_hton, in this particular case) resulting in
segfault.

Solution:
Fixed by calling THD::init_for_queries() (which accesses maria_hton)
only after the plugins have been initialized.

MDEV-8819: Failing assertion: block->page.space == page_get_space_id(page_align(ptr)) in file buf0buf.cc line 2551

Add error handling on page reading and do not try to access empty pages.

Merge downstream Debian packaging (MDEV-6284)

The fix for MDEV-8466 earlier fixed MDEV-8635 as well. Adding a test only.

- Add EXPLAIN/ANALYZE FORMAT=JSON handling for a few special cases.

introduced by the patch for MDEV-8466 and MDEV-8468.
Using --enable_prepare_warnings and --disable_prepare_warnings
around the affected query, to have the same warning in regular
and --ps mtr runs.

MDEV-8660 TIME(int_zerofill_column) returns a wrong result

MDEV-8832: Encryption meta data should not be stored when ENCRYPTED=DEFAULT and innodb-encrypt-tables=OFF

Item_string::clone_item() creates a new Item_string that
points exactly to the same buffer that the original one does.
Later, Item_string::print() uses c_ptr() for the original Item_string,
which reallocs the original buffer, and the clone remain with
the old freed buffer.
Refactoring the code not to use c_ptr() in Item_string::print().

Folloup: Made encryption rules too strict (and incorrect). Allow creating
table with ENCRYPTED=OFF with all values of ENCRYPTION_KEY_ID but create
warning that nondefault values are ignored. Allow creating table with
ENCRYPTED=DEFAULT if used key_id is found from key file (there was
bug on this) and give error if key_id is not found.

Failed attempt to load dynamic library with STB_GNU_UNIQUE symbol may corrupt
internal dynamic linker data sructures. This looks like libdl bug:
https://sourceware.org/bugzilla/show_bug.cgi?id=14577

In embedded mode "show plugins soname" fails to dlopen ha_mroonga.so (which
has STB_GNU_UNIQUE) due to undefined reference to wsrep_forced_binlog_format.
It crashes later in subsequent call to dlopen() from  pthread_exit().

Disabled plugins.show_all_plugins until dlopen() bug is fixed.