Ticket 49020 - do not treat missing csn as fatal
    
        This patch removes the automatic choice of an alternative csn when
        the calculated anchor csn is not found.
    
        In that case it does no longer go to fatal state but will retry later.
    
        It also adds a configuration parameter to thr replication agreement to
        allow to pick a "next best" anchorcsn if the original is not found to
        keep replicatio going.
    
        Reviewed by: Noriko, William