Fix warnings_checker.dart handling of multitests

tests/language_strong/hidden_import_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // Tests that dart: imports are implicitly hidden and cause warning on use.
 
 library hidden_import;
 
 import 'hidden_import_lib.dart';
 import 'hidden_import_lib.dart' as prefix;
 import 'dart:async';
 import 'dart:async' as prefix;
 
 main() {
-  new Future(); /// 01: static type warning
-  new prefix.Future(); /// 02: static type warning
+  new Future(); //# 01: static type warning
+  new prefix.Future(); //# 02: static type warning
 }