Fix warnings_checker.dart handling of multitests

tests/language_strong/compile_time_constant_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.
 
 class Bad {
   int foo;
   final int bar =
-      foo /// 01: compile-time error
+      foo //# 01: compile-time error
       -1;
   static const int toto =
-      bar /// 02: compile-time error
+      bar //# 02: compile-time error
       -3;
 }
 
 void use(x) {}
 
 main() {
   use(new Bad().bar);
   use(Bad.toto);
 }