When the function exits with an error it was not
freeing the local Unique class instance.
Fixed my making sure all the places where the function
returns from are freeing the Unique instance 

Bug#45243: crash on win in sql thread clear_tables_to_lock() -> free()
Bug#45242: crash on win in mysql_close() -> free()
Bug#45238: rpl_slave_skip, rpl_change_master failed (lost connection) for STOP SLAVE
Bug#46030: rpl_truncate_3innodb causes server crash on windows
Bug#46014: rpl_stm_reset_slave crashes the server sporadically in pb2

When killing a user session on the server, it's necessary to
interrupt (notify) the thread associated with the session that
the connection is being killed so that the thread is woken up
if waiting for I/O. On a few platforms (Mac, Windows and HP-UX)
where the SIGNAL_WITH_VIO_CLOSE flag is defined, this interruption
procedure is to asynchronously close the underlying socket of
the connection.

In order to enable this schema, each connection serving thread
registers its VIO (I/O interface) so that other threads can
access it and close the connection. But only the owner thread of
the VIO might delete it as to guarantee that other threads won't
see freed memory (the thread unregisters the VIO before deleting
it). A side note: closing the socket introduces a harmless race
that might cause a thread attempt to read from a closed socket,
but this is deemed acceptable.

The problem is that this infrastructure was meant to only be used
by server threads, but the slave I/O thread was registering the
VIO of a mysql handle (a client API structure that represents a
connection to another server instance) as a active connection of
the thread. But under some circumstances such as network failures,
the client API might destroy the VIO associated with a handle at
will, yet the VIO wouldn't be properly unregistered. This could
lead to accesses to freed data if a thread attempted to kill a
slave I/O thread whose connection was already broken.

There was a attempt to work around this by checking whether
the socket was being interrupted, but this hack didn't work as
intended due to the aforementioned race -- attempting to read
from the socket would yield a "bad file descriptor" error.

The solution is to add a hook to the client API that is called
from the client code before the VIO of a handle is deleted.
This hook allows the slave I/O thread to detach the active vio
so it does not point to freed memory.

server-tools/instance-manager/mysql_connection.cc:
  Add stub method required for linking.
sql-common/client.c:
  Invoke hook.
sql/client_settings.h:
  Export hook.
sql/slave.cc:
  Introduce hook that clears the active VIO before it is freed
  by the client API.

on SHOW CREATE TRIGGER + MERGE table

Problem: SHOW CREATE TRIGGER erroneously relies on fact
that we have the only underlying table for a trigger
(wrong for merge tables).

Fix: remove erroneous assert().


mysql-test/r/merge.result:
  Fix for bug #46614: Assertion in show_create_trigger() 
  on SHOW CREATE TRIGGER + MERGE table
    - test result.
mysql-test/t/merge.test:
  Fix for bug #46614: Assertion in show_create_trigger() 
  on SHOW CREATE TRIGGER + MERGE table
    - test case.
sql/sql_show.cc:
  Fix for bug #46614: Assertion in show_create_trigger() 
  on SHOW CREATE TRIGGER + MERGE table
    - unnecessary assert() removed as we may have more than 1 
  tables open e.g. for a merge table.

There is an inconsistency with DROP DATABASE|TABLE|EVENT IF EXISTS and
CREATE DATABASE|TABLE|EVENT IF NOT EXISTS. DROP IF EXISTS statements are
binlogged even if either the DB, TABLE or EVENT does not exist. In
contrast, Only the CREATE EVENT IF NOT EXISTS is binlogged when the EVENT
exists.  

This patch fixes the following cases for all the replication formats:
CREATE DATABASE IF NOT EXISTS.
CREATE TABLE IF NOT EXISTS,
CREATE TABLE IF NOT EXISTS ... LIKE,
CREAET TABLE IF NOT EXISTS ... SELECT.

sql/sql_insert.cc:
  Part of the code was moved from the create_table_from_items to select_create::prepare.
  When replication is row based, CREATE TABLE IF NOT EXISTS.. SELECT is binlogged if the table exists.

"CREATE TABLE TRANSACTIONAL PAGE_CHECKSUM ROW_FORMAT=PAGE accepted, 
does nothing".

Put back stubs for members of structures that are shared between
sql/ and pluggable storage engines. to not break ABI unnecessarily.
To be NULL-merged into 5.4, where we do break the ABI already.

not ready to run with innoplug-1.0.4.

PAGE_CHECKSUM ROW_FORMAT=PAGE accepted, does nothing"
Remove unused code that would lead to warnings when compiling
sql_yacc.yy.


sql/handler.h:
  Remove unused defines.
sql/sql_yacc.yy:
  Remove unused grammar.
sql/table.h:
  Remove unused TABLE members.

        
Replication SQL thread does not set database default charset to 
thd->variables.collation_database properly, when executing LOAD DATA binlog.
This bug can be repeated by using "LOAD DATA" command in STATEMENT mode.
        
This patch adds code to find the default character set of the current database 
then assign it to thd->db_charset when slave server begins to execute a relay log.
The test of this bug is added into rpl_loaddata_charset.test 

widely used, in replication (delete_allow_opened) and for named
pipe support. We do not support Win9x anymore.

The problem is that the lexer could inadvertently skip over the
end of a query being parsed if it encountered a malformed multibyte
character. A specially crated query string could cause the lexer
to jump up to six bytes past the end of the query buffer. Another
problem was that the laxer could use unfiltered user input as
a signed array index for the parser maps (having upper and lower
bounds 0 and 256 respectively).

The solution is to ensure that the lexer only skips over well-formed
multibyte characters and that the index value of the parser maps
is always a unsigned value.

mysql-test/r/ctype_recoding.result:
  Update test case result: ending backtick is not skipped over anymore.
sql/sql_lex.cc:
  Characters being analyzed must be unsigned as they can be
  used as indexes for the parser maps. Only skip over if the
  string is a valid multi-byte sequence.
tests/mysql_client_test.c:
  Add test case for Bug#45010

Problem 1:
When the 'Using index' optimization is used, the optimizer may still - after
cost-based optimization - decide to use another index in order to avoid using
a temporary table. But when this happens, the flag to the storage engine to 
read index only (not table) was still set. Fixed by resetting the flag in the 
storage engine and TABLE structure in the above scenario, unless the new index
allows for the same optimization.
Problem 2:
When a 'ref' access method was employed by cost-based optimizer, (when the column
is non-NULLable), it was assumed that it needed no initialization if 'quick' access
methods (since they are based on range scan). When ORDER BY optimization overrides 
the decision, however, it expects to have this initialized and hence crashes. 
Fixed in 5.1 (was fixed in 6.0 already) by initializing 'quick' even when there's 
'ref' access. 

mysql-test/r/order_by.result:
  Bug#46454: Test result.
mysql-test/t/order_by.test:
  Bug#46454: Test case.
sql/sql_select.cc:
  Bug#46454: 
  Problem 1 fixed in make_join_select()
  Problem 2 fixed in test_if_skip_sort_order()
sql/table.h:
  Bug#46454: Added comment to field.

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