Ticket 49287 - v3 extend csnpl handling to multiple backends
    
        The csn pending list mechanism failed if internal operation affected multiple backends
    
        This fix is an extension to the fix in ticket 49008, the thread local data now also contains
        a list of all affected replicas.
    
        http://www.port389.org/docs/389ds/design/csn-pending-lists-and-ruv-update.html
    
        Reviewed by: William, Thierry - thanks