anchor.diff:  %% Purpose: Convert process state when code is changed
   %% Returns: {ok, NewState}
   %%--------------------------------------------------------------------
  -code_change(OldVsn, State, Extra) ->
  +code_change(_OldVsn, State, _Extra) ->
       {ok, State}.
   
   %%--------------------------------------------------------------------
  
positive.code: %%          {stop, Reason, Reply, State}   | (terminate/2 is called)
  %%          {stop, Reason, State}            (terminate/2 is called)
  %%--------------------------------------------------------------------
  handle_call(Request, From, State) ->
      logger:log(error, "Registrar: Received unknown gen_server call : ~p", [Request]),
      {reply, {error, "Unknown gen_server call", State}}.
  
  
negative.code: %%          {stop, Reason}
  %%--------------------------------------------------------------------
  init([]) ->
      timer:apply_interval(60000, phone, remove_expired_phones, []),
      logger:log(debug, "Registrar started"),
      {ok, #state{}}.
  
  