Fix warnings_checker.dart handling of multitests

tests/language/unsupported_operators_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.
 
 // Test handling of unsupported operators.
 
 library unsupported_operators;
 
 class C {
   m() {
     print(
-          super === /// 01: compile-time error
+          super === //# 01: compile-time error
           null);
     print(
-          super !== /// 02: compile-time error
+          super !== //# 02: compile-time error
           null);
   }
 }
 
 void main() {
   new C().m();
   new C().m();
   print(
-        "foo" === /// 03: compile-time error
+        "foo" === //# 03: compile-time error
         null);
   print(
-        "foo" !== /// 04: compile-time error
+        "foo" !== //# 04: compile-time error
         null);
 }