In tables_ok(), when there is no table having "updating==TRUE" in the list,
    return that we don't replicate this statement (the slave is supposed to
    replicate *changes* only).
    In practice, the case can only happen for this statement:
    DELETE t FROM t,u WHERE ... ;
    tables_ok(t,u) will now return 0, which (check all_tables_not_ok())
    will give a chance to tables_ok(t) to run.