Fix warnings_checker.dart handling of multitests

tests/language_strong/const_instance_field_test.dart

 // Copyright (c) 2014, 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 const instance fields are compile-time errors.
 
 class C {
-  const field = 0; /// 01: compile-time error
+  const field = 0; //# 01: compile-time error
 }
 
 void main() {
   new C();
 }