Fix warnings_checker.dart handling of multitests

tests/language_strong/try_catch_test.dart

 // Copyright (c) 2011, 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.
 // VMOptions=--optimization-counter-threshold=10
 
 import "package:expect/expect.dart";
 
 class MyException { }
 
 class MyException1 extends MyException { }
@@ skipping 150 matching lines @@
 
   static void test12() {
     const x = const [];
     try {
       throw "up";
     } catch (e) {
       Expect.equals("up", e);
     } on String catch (e) {
       // Compile-time constants in unreachable catch blocks are still
       // compiled.
-      const y = x[0]; // /// 01: compile-time error
+      const y = x[0]; // //# 01: compile-time error
       Expect.fail("unreachable");
     }
   }
       
 
   static void testMain() {
     test1();
     test2();
     test3();
     test4();
     test5();
     test6();
     test7();
     test8();
     test9();
     test10();
     test11();
     test12();
   }
 }
 
 main() {
   for (var i = 0; i < 20; i++) {
     TryCatchTest.testMain();
   }
 }