Fix warnings_checker.dart handling of multitests

tests/language/unbalanced_brace_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.
 
 // Test syntax errors related to unterminated braces.
 
 class A {
   m() {
-  /* /// 01: compile-time error
+  /* //# 01: compile-time error
   }
   // */
 
-/* /// 02: compile-time error
+/* //# 02: compile-time error
 }
 // */
 
 class B {
 }
 
 main() {
   new A();
   new B();
 }