Import 898b5edfe757cb145960b8f3631029bfd5592119 from ctdb:

Import 898b5edfe757cb145960b8f3631029bfd5592119 from ctdb:
Author: Volker Lendecke <vl@samba.org>  2010-01-30 03:51:09

    tdb: fix an early release of the global lock that can cause data corruption

    There was a bug in tdb where the

                    tdb_brlock(tdb, GLOBAL_LOCK, F_UNLCK, F_SETLKW, 0, 1);

    (ending the transaction-"mutex") was done before the

                            /* remove the recovery marker */

    This means that when a transaction is committed there is a window where another
    opener of the file sees the transaction marker while the transaction committer
    is still fully functional and working on it. This led to transaction being
    rolled back by that second opener of the file while transaction_commit() gave
    no error to the caller.

    This patch moves the F_UNLCK to after the recovery marker was removed, closing
    this window.