Ticket #47412 - Modify RUV should be serialized in ldbm_back_modify/add
    
    Bug Description: Current ldbm_back_modify and _add allow RUV to
    update without respecting other threads in the backend's critical
    area. It gives a chance for 2 threads trying to modify RUV at the
    same time in the 2 different transactions which causes the DB
    deadlocks.
    
    Fix Description: This patch changes the policy for RUV to skip
    the backend serial lock.
    
    https://fedorahosted.org/389/ticket/47412
    
    Reviewed by Rich (Thank you!!)