Fix warnings_checker.dart handling of multitests

tests/language/const_constructor_test.dart

 // Copyright (c) 2012, 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.
 
 import "package:expect/expect.dart";
 
 class A<T> {
   final int x;
   const A.named() : x = 42;
   A() : x = null;
 }
 
 main() {
   Expect.equals(42, (const A<int>.named()).x);
   Expect.equals(42, (new A<int>.named()).x);
-  const A<int>(); /// 01: compile-time error
+  const A<int>(); //# 01: compile-time error
 }