post push fix, added test found a valgrind warning

Adding comments to some of the high-level functions in replication.

When substituting system constant functions with a constant result
the server was not expecting that the function may return NULL.
Fixed by checking for NULL and returning Item_null (in the relevant
collation) if the result of the system constant function was NULL.

The special TRUNCATE TABLE (DDL) transaction wasn't being properly
rolled back if a error occurred during row by row deletion. The
error can be caused by a foreign key restriction imposed by InnoDB
SE and would cause the server to erroneously issue a implicit
commit.

The solution is to rollback the transaction if a truncation via row
by row deletion fails, otherwise commit. All effects of a TRUNCATE 
ABLE operation are rolled back if a row by row deletion fails.

Problem: when the server reads a log_event from file, it should read
the post-header lengths from the format_description_log_event. Some
event types which currently have post-header length 0 did not do this,
and instead had a hard-coded zero length for the post-header. That
means the current server version will not be able to read future
versions of these events.
Fix: make the reader functions read the post-header.

The binlog_innodb test was sensitive to what tests ran before it.  Now run
FLUSH STATUS before performing operations that need to be checked.

sys_var_thd_ulong::update() was improperly casting an option value from
ulonglong to ulong before comparing it to the max allowed value.  On systems
where ulong and ulonglong are of different size, this caused values greater
than ULONG_MAX to wrap around (not be truncated to ULONG_MAX, which appears to
have been the intention of the original coder), and caused some checks to work
incorrectly.  This wasn't generally visible to the user, because later checks
would prevent the wrapped-around value from being used.  But it caused warning
messages to differ between 32- and 64-bit platforms.  Fix is to just remove the
cast.  Also added a DBUG_ASSERT to ensure that the value really is capped
properly before finally stuffing it into the ulong.

           locking type of temp table

The problem is that INSERT INTO .. SELECT FROM .. and CREATE
TABLE .. SELECT FROM a temporary table could inadvertently
overwrite the locking type of the temporary table. The lock
type of temporary tables should be a write lock by default.

The solution is to reset the lock type of temporary tables
back to its default value after they are used in a statement.

Added function to check for diff and return an error message if the utility is not present.
Previously, the way we did this didn't work on Windows, but did work on *Nix systems.

case.

Execution of queries containing the CASE function of
aggregate function like in "SELECT ... CASE ARGV(...) WHEN ..."
crashed the server.


The CASE function caches pointers to concrete comparison
functions for an each pair of types of CASE-WHERE clause
parameters, i.e. for the "CASE INT_RESULT WHERE REAL_RESULT
THEN ... WHERE DECIMAL_RESULT ... END" function call it
caches comparisons for INT_RESULT with REAL_RESULT and
for INT_RESULT with DECIMAL_RESULT. Usually a result
type is known after a call to the fix_fields function,
however, the setup_copy_fields function call may
wrap aggregate items with Item_copy_string that has
STRING_RESULT result type, so setup_copy_fields may
change argument result types of the CASE function after
call to Item_func_case::fix_fields/fix_length_and_dec.
Then the Item_func_case::find_item function tries to
use comparison function for unexpected pair of the
STRING_RESULT and some other type - that caused
an assertion failure of server crash.

The Item_func_case::fix_length_and_dec function has
been modified to take into account possible STRING_RESULT
result type in the presence of aggregate arguments of
the CASE function.

Disabled rpl_binlog_corruption since it requires the new mtr,
which only exists in 5.1-rpl / 6.0-rpl.
Please re-enable the test in 5.1-rpl / 6.0-rpl.

Problem: When an Incident_log_event contains a bad incident number on disk,
the server crashes with an assertion.
Fix: Don't validate input with assertions. Use errors.

The problem: data file can not be deleted on win because
there is another opened instance of this file.
Data file might be opened twice, on table opening stage and
during write_row execution. We need to close both instances
to satisfy Win.

Added global status variable 'Queries' which represents
total amount of queries executed by server including
statements executed by SPs.
note: It's old behaviour of 'Questions' variable.