Fix warnings_checker.dart handling of multitests

tests/language/redirecting_factory_malbounded_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.
 
 class Foo<T> extends Bar<T> {
 
   factory Foo() = Bar;
 
   Foo.create() : super.create() { }
 }
 
 class Bar<T
-            extends num // /// 01: static type warning, dynamic type error
+            extends num // //# 01: static type warning, dynamic type error
                        > {
   factory Bar() {
     return new Foo<T>.create();
   }
 
   Bar.create() { }
 }
 
 main() {
   new Foo<String>();
 }