def add_del_on_list(key, to_add, to_remove)
      result = req_list(new_req_list().add_add_del_on_list(key, to_add, to_remove))[0]
      process_result_add_del_on_list(result)
    end
def add_del_on_list(key, to_add, to_remove)
      result = req_list(new_req_list().add_add_del_on_list(key, to_add, to_remove))[0]
      process_result_add_del_on_list(result)
    end
Issues a add_del_on_list operation to scalaris and adds it to the
 current transaction.
 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.