anchor.diff:    Future<WampRegistration> register(String uri, WampProcedure proc,
         [Map options = const <String, dynamic>{}]) {
       final cntl = new StreamController<int>();
  -    final code = _flightCode(cntl);
  -    _ws.add(JSON.encode([WampCode.register, code, options, uri]));
  +    _goFlight(cntl, (code) => [WampCode.register, code, options, uri]);
       return cntl.stream.last.then((regid) {
         _registrations[regid] = proc;
         return new WampRegistration(regid);
  
positive.code:     _inflights[code] = val;
      return code;
    }
  }
  
negative.code:       Map<String, dynamic> params = const <String, dynamic>{},
        Map options = const <String, dynamic>{}]) {
      final cntl = new StreamController<WampArgs>();
      _goFlight(
          cntl, (code) => [WampCode.call, code, options, uri, args, params]);
      return cntl.stream.last;
    }
  
  