The problem reported as MDEV-5444.

- include metadata_lock_info plugin into debian packages
- ignore metadata_lock_info plugin in mysqld--help test
- let test suite run with built-in metadata_lock_info plugin

Removed unused_tables, find LRU object by timestamp instead.

- tc_acquire_table and tc_release_table do not access
  TABLE_SHARE::tdc.used_tables anymore
- in tc_acquire_table(): release LOCK_tdc after we relase LOCK_open
  (saves a few CPU cycles in critical section)
- in tc_release_table(): if we reached table cache threshold, evict
  to-be-released table without moving it to unused_tables. unused_tables
  must be empty at this point.

fix the element deleting logic for roles_mappings_hash

use generic restore_ptr_backup() approach

MDEV-4403 Attempting to use cassandra storage engine causes "service 'my_snprintf_service' interface version mismatch"

When a DSO is loaded we rewrite service pointers to point to the actual service structures.
But when a DSO is unloaded, we have to restore their original values, in case this DSO
wasn't removed from memory on dlclose() and is later loaded again.

* comments from WL#5602 in sql_acl.cc
* rename global memroots in sql_acl.cc
* remove the second empty lex string constant

  Remove unused code (that should not have been merged)
  Add protocol extension (that should have been merged)
  Fix bugs (see pack.c)

Patially merge WL#5917, to understand v2 row events

fix a copy-paste error, introduced in role refactoring

fix the code to compile with clang. fix warnings too.

include/probes_mysql_nodtrace.h:
  clang++ doesn't like numeric _constants_ being used in ||
  (it suspects that the intention was | ). Boolean constants are ok.
sql/hostname.cc:
  only used in DBUG_ASSERT
sql/item.cc:
  str_to_time and str_to_datetime return bool, not MYSQL_TIMESTAMP_xxx
sql/item_func.cc:
  str_to_datetime_with_warn() returns bool, not MYSQL_TIMESTAMP_xxx
storage/cassandra/CMakeLists.txt:
  CMAKE_CXX_FLAGS can be empty
storage/connect/odbconn.cpp:
  HWND is void*
storage/connect/user_connect.h:
  deprecated on FreeBSD and unused anyway
storage/connect/value.cpp:
  bad characters inside. unused.
storage/spider/spd_trx.cc:
  clang++ warns that memset will also overwrite vtbl. it might be as well a good idea,
  as it asserts that the object will only be used as a storage.
  silence the warning.

when frm file exists, but the table does not.

In recover_from_failed_open(), allow the discovery
to fail without an error, when
open_strategy == TABLE_LIST::OPEN_IF_EXISTS.

merged from 5.6:
Bug#14521864: MYSQL 5.1 TO 5.5 BUGS PARTITIONING
Bug#16589511: MYSQL_UPGRADE FAILS TO WRITE OUT ENTIRE ALTER TABLE ... ALGORITHM= ... STATEMENT
Bug#16274455: CAN NOT ACESS PARTITIONED TABLES WHEN DOWNGRADED FROM 5.6.11 TO 5.6.10

plus minor changes from 5.6, mainly comments

Fixing include/ctype_datetime.inc not to depend on the current time zone.

            into 10.0

            into 10.0

"mtr ctype_ldml" failed when compiled with "gcc -funsigned-char".
Changing the code not to depend on the signed/unsigned compiler defaults
for the "char" data type.

Fixed.

Fixed.

in the code merged from MySQL-5.6:

  const CHARSET_INFO* -> CHARSET_INFO*

(CHARSET_INFO already has the "const" qualifier in MariaDB, inlike in MySQL)

Applied a patch from Philip Hazel implementing the non-standard
syntax for word boundaries in PCRE, for compatibility with the
old Henry Spencer's regex library.

modified:
  storage/connect/valblk.cpp

modified:
  storage/connect/ha_connect.cc
  storage/connect/value.cpp

- Fix the way GetPlug works (was not updating xp)

modified:
  storage/connect/ha_connect.cc

modified:
  storage/connect/odbconn.cpp

- Prepare Value and Valblk to support unsigned data types
  (not operational yet)

modified:
  storage/connect/colblk.cpp
  storage/connect/filamvct.cpp
  storage/connect/myconn.cpp
  storage/connect/plgdbutl.cpp
  storage/connect/tabdos.cpp
  storage/connect/tabodbc.cpp
  storage/connect/tabvct.cpp
  storage/connect/valblk.cpp
  storage/connect/valblk.h
  storage/connect/value.cpp
  storage/connect/value.h
  storage/connect/xindex.cpp