Fix warnings_checker.dart handling of multitests

tests/language/const_switch2_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.
 
 import 'package:expect/expect.dart';
 
 int main() {
   var a = [1,2,3][2];
   switch (a) {
-    case 0.0: //           /// 01: compile-time error
-      print("illegal"); // /// 01: continued
+    case 0.0: //           //# 01: compile-time error
+      print("illegal"); // //# 01: continued
     case 1:
       print("OK");
   }
 }