cherry-pick the upstream fix

commit d4ba10184cd7bde9c31c610e664ecd0c93605c46
Author: Sujatha Sivakumar <sujatha.sivakumar@oracle.com>
Date:   Wed Jul 2 11:34:11 2014 +0530

    Bug#17453826:ASSERTION ERROR WHEN SETTING FUTURE BINLOG
    FILE/POS WITH SEMISYNC

    Problem:
    ========
    When DMLs are in progress on the master stopping a slave and
    setting ahead binlog name/pos will cause an assert on the
    master.
    ...