WHERE DEFAULT(col)
It seems this was not covered yet.

Step 2c:

After discussion with Igor, it appeared that Item_field and Item_ref
could not appear in this context in the old function build_equal_item_for_cond:

  else if (cond->type() == Item::FUNC_ITEM ||
           cond->real_item()->type() == Item::FIELD_ITEM)

The part of the condition checking for Item_field::FIELD_ITEM was a dead code.
- Moving implementation of Item_ident_or_func_or_sum::build_equal_items()
to Item_func::build_equal_items()
- Restoring deriving of Item_ident and Item_sum_or_func from Item_result_field.
  Removing Item_ident_or_func_or_sum.

Problem was that std::vector was allocated using calloc instead of
new, this caused vector constructor not being called and vector
metadata not initialized.

C++03 seem to require default constructor for const objects even though they're
fully initialized. There is defect report for this:
http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#253

Apparently some compilers (e.g. gcc) addressed this defect report, while some
(e.g. clang) did not.

Added empty default constructor to MDL_scoped_lock and MDL_object_lock classes.

Also replaced lf_hash_search_using_hash_value() with lf_hash_search(). The
latter will call mdl_key->hash_value() anyway.

MDEV-7950 Item_func::type() takes 0.26% in OLTP RO (Step#2)

- Item_ref was doing unnecessary extra job after the "MDEV-7950 Step#2" patch.
  Fallback to Item::build_equal_items() if real_type() is not FIELD_ITEM.
  Note, Item_ref::build_equal_items() will most likely be further simplified.
  Waiting for Sanja and Igor to check a possibly dead code.

- Safety: Adding Item_sum::build_equal_items() with ASSERT, as Item_sum
  should never appear in build_equal_items() context.

Backport into 10.0

Step#2:

1. Removes the function build_equal_items_for_cond() and
   introduces a new method Item::build_equal_items() instead,
   with specific implementations in the following Items:

   Item  (the default implementation)
   Item_ident_or_func_or_sum
   Item_cond
   Item_cond_and

2. Adds a new abstract class Item_ident_or_func_or_sum,
   a common parent for Item_ident and Item_func_or_sum,
   as they have exactly the same build_equal_items().

3. Renames Item_cond_and::cond_equal to Item_cond_and::m_cond_equal,
   to avoid confusion between the member and local variables named
   "cond_equal".

The slave SQL thread was clearing serial_rgi->thd before deleting
serial_rgi, which could cause access to NULL THD.

The clearing was introduced in commit
2e100cc5 and is just plain wrong. So revert
that part (single line) of that commit.

Thanks to Daniel Black for bug analysis and test case.

to constructor Create_field::Create_field().

TODO: move some methods from Item to Type_std_attributes.

MDEV-7130: MASTER_POS_WAIT(log_name,log_pos,timeout,"connection_name") hangs, does not respect the timeout

Changed also arg_count check for connection_name to prevent same bug
if fifth argument is introduced in future

between Item_func, Item_sum, Item_row.

MDEV-8031: Parallel replication stops on "connection killed" error (probably incorrectly handled deadlock kill)

There was a rare race, where a deadlock error might not be correctly
handled, causing the slave to stop with something like this in the error
log:

150423 14:04:10 [ERROR] Slave SQL: Connection was killed, Gtid 0-1-2, Internal MariaDB error code: 1927
150423 14:04:10 [Warning] Slave: Connection was killed Error_code: 1927
150423 14:04:10 [Warning] Slave: Deadlock found when trying to get lock; try restarting transaction Error_code: 1213
150423 14:04:10 [Warning] Slave: Connection was killed Error_code: 1927
150423 14:04:10 [Warning] Slave: Connection was killed Error_code: 1927
150423 14:04:10 [ERROR] Error running query, slave SQL thread aborted. Fix the problem, and restart the slave SQL thread with "SLAVE START". We stopped at log 'master-bin.000001 position 1234

The problem was incorrect error handling. When a deadlock is detected, it
causes a KILL CONNECTION on the offending thread. This error is then later
converted to a deadlock error, and the transaction is retried.

However, the deadlock error was not cleared at the start of the retry, nor
was the lingering kill signal. So it was possible to get another deadlock
kill early during retry. If this happened with particular thread
scheduling/timing, it was possible that the new KILL CONNECTION error was
masked by the earlier deadlock error, so that the second kill was not
properly converted into a deadlock error and retry.

This patch adds code that clears the old error and killed flag before
starting the retry. It also adds code to handle a deadlock kill caught in a
couple of places where it was not handled before.

Fix a silly typo that caused the test to occasionally fail.

This was a regression from the patch for MDEV-7668.

A test was incorrect, so the slave would not properly handle re-using
temporary tables, which lead to replication failure in this case.

Conflicts:
	mysql-test/suite/multi_source/multisource.result
	sql/sql_base.cc

Removing "Field *result_field" from Item_field and Item_ref,
and deriving Item_ident and Item_ref from Item_result_field
instead.

as the other decendants of Item_result_field (Item_avg_field,
Item_variance_field, Item_cache_wrapper) don't need fix_length_and_dec().

- Adding a new class Item_args, represending regular function or
  aggregate function arguments array.

- Adding a new class Item_func_or_sum,
  a parent class for Item_func and Item_sum

- Moving Item_result_field::name() to Item_func_or_sum(),
  as name() is not needed on Item_result_field level.

Post-fix : A typo and better error handling.

Add some suppressions that were missing. They are for if a STOP SLAVE is
executed early during IO thread startup, when it is negotiating with the
master. The master connection may be killed in the middle of a
mysql_real_query(), which is not a test failure if it is a network error.

This also caught one real code error, fixed with this commit: The I/O thread
would fail to automatically reconnect if a network error happened while
fetching the value of @@GLOBAL.gtid_domain_id.