Fix warnings_checker.dart handling of multitests

tests/language/internal_library_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.
 
 // Test that a private library cannot be accessed from outside the platform.
 
 library internal_library_test;
 
 import 'dart:core'; // This loads 'dart:_foreign_helper' and 'patch:core'.
-import 'dart:_foreign_helper'; /// 01: compile-time error
+import 'dart:_foreign_helper'; //# 01: compile-time error
 
-part 'dart:_foreign_helper'; /// 02: compile-time error
+part 'dart:_foreign_helper'; //# 02: compile-time error
 
 void main() {
-  JS('int', '0'); /// 01: continued
-  JS('int', '0'); /// 02: continued
+  JS('int', '0'); //# 01: continued
+  JS('int', '0'); //# 02: continued
 }