Problem: in 5.0 'check table for upgrade' doesn't detect
incompatible collation changes made in 5.0.48.

Fix: backport #39585 fix to 5.0

Altering how MTR checks global variable status to exclude timestamp
Changed SQL statements to update style.

Problem was usage of read_range_first with an empty key.

Solution was to not to give a key if it was empty.

ONLY_FULL_GROUP_BY

The check for non-aggregated columns in queries with aggregate function, but without
GROUP BY was treating all the parts of the query as if they are in the SELECT list.
Fixed by ignoring the non-aggregated fields in the WHERE clause.

- restore original state of event_scheduler at the end of the test
- minor fixes around comments, formatting

the problem is the same as reported in bug#20835,
so the fix is backport of bug#20835 patch.

returns truncated results

Problem: performig conversion from {INT, DECIMAL, REAL} to CHAR
we incorrectly set its max length in some cases that may lead
to truncated results returned.

Fix: properly set CONVERT({INT, DECIMAL, REAL}, CHAR) result's
max length.

temporarily if yassl maintainer has plans for other error handling.

variable settings (rpl_sys)

Problem: under certain conditions (e.g. user variables usage in triggers)
accessing a user defined variable we may use a variables hash table that
belongs to already deleted thread. It happens if
thd= new THD;
has the same address as just deleted thd as we use
if (stored_thd == thd)
to check.
That may lead to unpredictable results, server crash etc.

Fix: use thread_id instead of thd address to distinguish threads.

Note: no simple and repeatable test case.

Problem: memory leak occurs when we open a federated table
that has its share in the hash.

Fix: free not used memory.

Note: the fix should NOT be merged to 5.1 (the code changed).

set but is ignored".
                                  
This patch makes @@session.max_allowed_packed and
@@session.net_buffer_length read-only as suggested in the bug
report. The user will have to use SET GLOBAL (and reconnect)
to alter the session values of these variables.
                            
The error string ER_VARIABLE_IS_READONLY is introduced.
                            
Tests are modified accordingly.

The test itself is not faulty. The testcase timeout
problem happens if this IMHO mid size resource
(space in vardir, virtual memory, amount of disk I/O)
consuming test meets a weak (excessive disk I/O caused
by parallel applications or paging) testing box.

The modifications:
- Move the most time and disk I/O consuming subtest
  for Bug 1820 into its own script (multi_update2)
  This will reduce the likelihood that we exceed the
  testcase timeout.
- Replace error numbers with error names
- Minor improvements of the formatting

- 

Cache size  is truncated via 32bit ulong  in  ha_init_key_cache() and 
ha_resize_key_cache() 

This change fixes the cast to size_t instead of ulong. This cast is safe,
because key_buffer_size parameter is limited to SIZE_T_MAX

   additional fix - the 'debug' keyword removed

    That's a Win-specific error.
    When we create libmysqld.dll we have many libraries like mysys, dbug,
    strings, etc linked into that dll, so the application built upon
    this library shouldn't link these libraries to itself, rather use
    those inside the dll.

    Fixed by redirecting calls into the libmysqld.dll

per-file comments:
  dbug/dbug.c
Bug#38293 Libmysqld crash in mysql_library_init if language file missing
    fake _db_something definitions added

  include/my_dbug.h
Bug#38293 Libmysqld crash in mysql_library_init if language file missing
  fake _db_something declarations added

  libmysqld/examples/CMakeLists.txt
Bug#38293 Libmysqld crash in mysql_library_init if language file missing
    superfluous libraries removed from linking

  libmysqld/libmysqld.def
Bug#38293 Libmysqld crash in mysql_library_init if language file missing
    set of mysys functions added to the export section