Desc:- This will split Alter into 2 different commits. START ALTER and COMMIT
/ROLLBACK ALTER , Start Alter will be written in binlog as soon as we get the
locks for the table, alter will proceeds as usual and at the time of writing
binlog if alter is successful we will write COMMIT Alter other wise ROLLBACK
Alter.

Implementation details are in develop list
https://lists.launchpad.net/maria-developers/msg12067.html