More fixes for test failures in Buildbot:

 - Do not run crashing test in Valgrind.

 - FLUSH TABLES did not work to avoid errors about not closed tables when
   crashing server. Suppress the messages instead.

 - Rewrite multi-source test case to only start one pair of slave threads at a
   time, to work-around the bug MDEV-4352.

More fixes for race conditions in test cases.

Fix yet another race in the rpl_gtid_startpos test case.

Implement include/wait_for_purge.inc to purge binary logs; we need to
retry the purge multiple times until it succeeds in removing all the logs
we want, as binlog dump threads can be slow to stop on loaded machines and
hold back purge of logs that are still referenced by the thread.

Add tests crashing the slave in the middle of replication and checking that
replication picks-up again on restart in a crash-safe way.

Fix silly code that causes crash by inserting uninitialised data into a hash.

Fix some test case races and .result file updates, found with Buildbot.

Test crashing the master, check that it recovers the binlog state.

Fix one bug introduced by previous commit (crash-recoved binlog state was
overwritten by loading stale binlog state file).

Fix Windows build error.

Implement test case rpl_gtid_stop_start.test to test normal stop and restart
of master and slave mysqld servers.

Fix a couple bugs found with the test:

 - When InnoDB is disabled (no XA), the binlog state was not read when master
   mysqld starts.

 - Remove old code that puts a bogus D-S-0 into the initial binlog state, it
   is not correct in current design.

 - Fix memory leak in gtid_find_binlog_file().

When slave requested to start at some GTID, and that GTID was the very
last event (within its replication domain) in some binlog file, we did
not allow the binlog dump thread on the master to start from the
beginning of a following binlog file. This is a problem, since the
binlog file containing the GTID is likely to be purged if the
replication domain is unused for long.

With this fix, if the Gtid list event at the start of a binlog file
contains exactly the GTID requested by the slave, we allow to start
the binlog dump thread from this file, taking care not to skip any
events from that domain in the file.

Fix bug that RESET SLAVE did not reset Using_Gtid back to 0.

Fix MDEV-4329. When user does CHANGE MASTER TO
MASTER_GTID_POS='<explicit GTID state>', we check that this state
does not conflict with the binlog. But the code forgot to give an
error in the case where a domain was completely missing from the
requested position (eg. MASTER_GTID_POS='').

Silence compiler warning.

Fix missing error check for applying Gtid_log_event.

Fix a couple compiler warnings.

Fix remaining two sporadic test failures in the full test suite:

 - Remove crash in DBUG_ASSERT() in _db_flush() (bug also exists in main
   tree).

 - Fix locking order violation for LOCK_status by temporarily unlocking it
   while locking LOCK_active_mi (like a similar fix for
   LOCK_global_variables).

Adjust full test suite to work with GTID.

Huge patch, mainly due to having to update .result file for all SHOW BINLOG
EVENTS and mysqlbinlog outputs, where the new GTID events pop up.

Everything was painstakingly checked to be still correct and valid .result
file updates.

Fix checksums for the new GTID events (reported by Pavel Ivanov).
Fix printing of GTID_LIST_EVENT.

Fix 3 small issues reported by Pavel Ivanov.

Fix error handling when record_gtid() fails to update the
mysql.rpl_slave_state table.

Fix MDEV-4278: Slave does not check that master understands GTID.

Now the slave will abort with a suitable error if an attempt is made to connect
with GTID to a master that does not support GTID.

Fix MDEV-4275 - I/O thread restart duplicates events in the relay log.
The first time we connect to master after CHANGE MASTER or restart, we connect
from the GTID position. But then subsequent reconnects or IO thread restarts
reconnect with the old-style file/offset binlog pos from where it left off at
last disconnect. This is necessary to avoid duplicate events in the relay
logs, as there is nothing that synchronises the SQL thread update of GTID
state (multiple threads in case of multi-source) with IO thread reconnects.

Test cases.

Some small cleanups and fixes.

Fix things so that a master can switch with MASTER_GTID_POS=AUTO to a slave
that was previously running with log_slave_updates=0, by looking into the
slave replication state on the master when the slave requests something not
present in the binlog.

Be a bit more strict about what position the slave can ask for, to avoid some
easy-to-hit misconfiguration errors.

Start over with seq_no counter when RESET MASTER.

After-rebase fixes. Rebase was done to be able to build on top
of the binlog background thread of MDEV-532.

Add a missing check for correct table definition.

Move a bunch of GTID specific code into new file rpl_gtid.cc. Make libmysqld build.

Improvements to record_gtid():

 - Check for correct table definition of mysql.rpl_slave_state
 - Use autocommit, to save one call to ha_commit_trans()
 - Slightly more efficient way to set table->write_set
 - Use ha_index_read_map() to locate rows to support any storage engine.

Extend table definition checking to also be able to check for correct
definition of the primary key.

Fix that CHANGE MASTER ... MASTER_GTID_POS="" works to start from the very
beginning of the binary log (with test case).

Fix that not finding the requested GTID position in master binlog results in
fatal error, not endless connect retry.

Add test case demonstrating multi-source replication with GTID.

Test that we can move from being slave of two masters to be a slave
deeper down in the hierarchy (of a higher-up multi-source slave),
and vice versa.

Remove the two-component form of GTID with implicit domain_id=0, as it
is likely to cause more confusion than help.

Give a better error for CHANGE MASTER ... MASTER_GTID_POS='gtid,gitd,...'
when two specified GTIDs have conflicting domain_id.

Fix lock order violation. Make sure we temporarily release
LOCK_global_system_variables before taking LOCK_active_mi.
Otherwise we get a lock dependency cycle when we use
open_tables() under LOCK_active_mi.

 - Fix skipping initial MyISAM DML when connecting using GTID.

 - Fix RESET MASTER not clearing in-memory binlog state.

 - Fix not reading standalone flag in Gtid_log_event::peek().

 - Fix skipping DDL that the slave has already seen when using GTID position.

 - Fix that binlog_gtid_pos() (and hence slave connect) does not work
   correctly in the very first binlog file (due to not logging empty
   Gtid_list_log_event).

 - Remove one instance of the stupid domain_id-0-is-implicit.

 - Rename the confusing Gtid_Pos_Auto in SHOW SLAVE STATUS to Using_Gtid.

 - Fix memory leak.

Fix crash in binlog_gtid_pos('', 4) (and thus slave connect) when master does not
have binlog enabled.

 - Add first basic mysql-test-run test case which tests switch to new master
   using MASTER_GTID_POS=AUTO.

 - When we connect with GTID, do not use any old relay logs, as they may
   contain the wrong events or be corrupt after crash.

 - Fix old bug that fails replication if we receive a heartbeat event
   immediately after an event was omitted in the stream from the master.

 - Fix rpl_end to clear Gtid_Pos_Auto, to keep check_testcase happy.

Fix memory leak.

 - Fix that slave GTID state was updated from the wrong place in the code,
   causing random crashing and other misery.

 - Fix updates to mysql.rpl_slave_state to not go to binlog (this would cause
   duplicate key errors on the slave and is generally the wrong thing to do).

Fix initial loading of mysql.rpl_slave_state, the code had several
issues.

Some very basic MTR stuff, more to come.

Fix things so that GTID state on slave is updated also for
non-XID event groups (ie. DDL and MyISAM DML).

Implement CHANGE MASTER TO ... MASTER_GTID_POS = "x-y-z,a-b-c".

Display replication slave gtid state in SHOW ALL SLAVES STATUS.

Slave now loads the GTID state from the master when connecting with
old-style filename/offset position.

This allows the user to use MASTER_GTID_POS=AUTO on next CHANGE MASTER
without any other action needed.