This is a backport of
Bug #46860 Crash/segfault using EXPLAIN EXTENDED on query using UNION in subquery.


mysql-test/r/explain.result:
  Remove the extended Note, since explain returns error.
  New test case.
mysql-test/r/func_gconcat.result:
  Remove the extended Note, since explain returns error.
mysql-test/r/subselect3.result:
  Remove the extended Note, since explain returns error.
mysql-test/t/explain.test:
  New test case.
sql/sql_parse.cc:
  Skip the extended description if we have an error.

  configuration wizard to fail

Made the fields mysql.user.plugin and mysql.user.authentication_string
nullable to conform with some older clients doing inserts instead of 
using the commands.

+
Bug#11766500 - 59624: FUNCS_1 SUITE TESTS FAILING WITH RESULT DIFFERENCE WHEN RUN USING EMBEDDED MODE
      
Updating result files for embedded mode 

Bug#11766500 - 59624: FUNCS_1 SUITE TESTS FAILING WITH RESULT DIFFERENCE WHEN RUN USING EMBEDDED MODE
      
Updating result files

Regression from bug#11766232.
m_last_part could be set beyond the last partition.
Fixed by only setting it if within the limit.
Also added check in print_error.

Fixed test suite failures when the auth plugin is not compiled in.

Added the cleanup code.
Extended mysql_client_test to take --plugin-dir and --default_auth.
Added a C test case.

                with no .cnf or .ini extension.

Fix for this bug was pushed as part of Bug#11765482.


mysql-test/r/mysqladmin.result:
  Added test case for Bug#11766184.
mysql-test/t/mysqladmin.test:
  Added test case for Bug#11766184.

Problem: the test had not been updated after BUG#49978 was pushed
Fix: add 'set $rpl_only_running_threads= 1' to the end of the test
and update the result file.
Also, use include/assert.inc for an assertion (instead of relying
on result file comparison).
Also, move 'set @@global.slave_net_timeout' forwards, to get rid
of a warning.


mysql-test/suite/large_tests/r/rpl_slave_net_timeout.result:
  updated result file
mysql-test/suite/large_tests/t/rpl_slave_net_timeout.test:
   - Got rid of warning "The requested value for the heartbeat period
     exceeds the value of `slave_net_timeout' seconds. A sensible
     value for the period should be less than the timeout." by
     changing order of "set slave_net_timeout" and
     "change master to master_heartbeat_period".
   - replaced result file comparison by include/assert.inc
   - added "let $rpl_only_running_threads= 1"

Currently, rpl_semi_sync is failing in PB due to the warning message:

  "Slave SQL: slave SQL thread is being stopped in the middle of "
  "applying of a group having updated a non-transaction table; "
  "waiting for the group completion ..."

The problem started happening after the fix for BUG#11762407 what was
automatically suppressing some warning messages.

To fix the current issue, we suppress the aforementioned warning message
and exploit the opportunity to make the sentence clearer.

Automerge: mysql-5.1 --> mysql-5.5 

      
There is a race between two threads: user thread and the dump
thread. The former sets a debug instruction that makes the latter wait
before processing an Xid event. There can be cases that the dump
thread has not yet processed the previous Xid event, causing it to
wait one Xid event too soon, thus causing sync_slave_with_master never
to resume.
      
We fix this by moving the instructions that set the debug variable
after calling sync_slave_with_master.