MDEV-5789: race between rpl_parallel_change_thread_count and slave start upon server start without --skip-slave-start

Make sure to signal the condition variable for the thread pool after
the new threads have been added to the pool.

Thanks to user nanyi607rao, who reported this bug on maria-developers@.

When an rpl_group_info object was returned from the free list, the
rgi->deferred_events_collecting and rgi->deferred_events was not correctly
re-inited. Additionally, the rgi->deferred_events was incorrectly freed in
free_rgi(), which causes unnecessary malloc/free (or crash when re-init is not
done).

Thanks to user nanyi607rao, who reported this bug on maria-developers@.

This constant uses my_time.h, which inclusion is not desirable in nt_servc.cc

Reduced number of my_hash_sort_bin() calls from 4 to 1 per query.
Reduced number of memory accesses done by my_hash_sort_bin().

Details:
- let MDL subsystem use pre-calculated hash value for hash
  inserts and deletes
- let table cache use pre-calculated MDL hash value
- MDL namespace is excluded from hash value calculation, so that
  hash value can be used by table cache as is
- hash value for MDL is calculated as resulting hash value + MDL
  namespace
- extended hash implementation to accept user defined hash function

- MariaDB-5.5 part of the fix: since we can't easily fix query optimization for I_S tables, 
  run the affected-tablespaces query with semijoin=off. It happens to have a good query plan
  with that setting.
[This is a forward-port to MariaDB 10.0]

- Removed double call to trans_begin() for GTID BEGIN event
- Don't set OPTION_BEGIN before calling trans_begin() as this causes extra work in trans_begin()

sql/log_event.cc:
  Removed double call to trans_begin for GTID BEGIN event.
  Don't set OPTION_BEGIN before calling trans_begin() as this causes extra work in trans_begin().
  This was done by removing parsing of "BEGIN" and instead executing trans_begin() direct.
  This is much faster, but we lost the ability logging of possible slow "BEGIN" statements. As this should never happen it can be ignored.

mysql-test/suite/rpl/t/rpl_heartbeat_basic.test:
  Added sync_slave_with_master to remove timing problem

Patch from Tomas Matejicek

Add missing error code to is_networ_error(), to allow slave to
automatically attempt reconnection also in this case.

The problem was when a GTID event was part of a group commit, and so contained
a commit id. The code that replaces GTID with a BEGIN event for old slaves did
not correctly handle this case.

Fix the code so that the GTID with commit id can also be properly replaced
with a BEGIN query event. The extra two bytes are in the BEGIN event replaced
with a dummy, empty time zone string.

- Make do_fill_table() use join_tab->cache_select->cond if it is present.  When 
  join_tab->cache_select->cond is present, join_tab->select_cond doesn't have any 
  conditions that are usable for I_S optimizations.

Older master has no GTID events, so such events are not available for
deciding on scheduling of event groups and so on.

With this patch, we run such events from old masters single-threaded, in the
sql driver thread.

This seems better than trying to make the parallel code handle the data from
older masters; while possible, this would require a lot of testing (as well as
possibly some extra overhead in the scheduling of events), which hardly seems
worthwhile.

- Fix valgrind failure: make test_if_order_by_key() account for extended keys 
  feature.

With parallel replication, there can be any number of events queued on
in-memory lists in the worker threads.

For normal STOP SLAVE, we want to skip executing any remaining events on those
lists and stop as quickly as possible.

However, for START SLAVE UNTIL, when the UNTIL position is reached in the SQL
driver thread, we must _not_ stop until all already queued events for the
workers have been executed - otherwise we would stop too early, before the
actual UNTIL position had been completely reached.

The code did not handle UNTIL correctly, stopping too early due to not
executing the queued events to completion. Fix this, and also implement that
an explicit STOP SLAVE in the middle (when the SQL driver thread has reached
the UNTIL position but the workers have not) _will_ cause an immediate stop.

MDEV-5748 Assertion `status_var.memory_used == 0' fails on disconnect after opening an OQGRAPH table

make sure MY_THREAD_SPECIFIC is not set for memroot that can be
transferred between threads

MDEV-5674 Valgrind warnings "Conditional jump or move depends on uninitialised value" in create_sort_index with small sort_buffer_size

*found_rows wasn't initialized when filesort() failed
(it didn't matter, but valgrind was unhappy)

use the Alter_inplace_info::ALTER_COLUMN_OPTION flag if
field/column flags were altered.

change ha_example to use check_if_supported_inplace_alter() instead
of obsolete check_if_incompatible_data()

parser: error out on empty role names

don't forget to initialize ORDER::fast_field_copier_setup

After constant row substitution some field items become constant items.
The range analyzer should take into account this fact when looking for
ranges.

Fix ha_table_exists() to take discovery into account correctly.
It must be able to discover both table existence (when no frm is
found) and table non-existance (when frm was found).

apply the upstream patch