def add_del_on_list(key, to_add, to_remove)
      result = @conn.call(:add_del_on_list, [key, to_add, to_remove])
      @conn.class.check_fail_abort(result)
      @conn.class.process_result_add_del_on_list(result)
    end
def add_del_on_list(key, to_add, to_remove)
      result = @conn.call(:add_del_on_list, [key, to_add, to_remove])
      @conn.class.check_fail_abort(result)
      @conn.class.process_result_add_del_on_list(result)
    end
Changes the list stored at the given key, i.e. first adds all items in
 to_add then removes all items in to_remove.
 Both, to_add and to_remove, must be lists.
 Assumes en empty list if no value exists at key.