Fix warnings_checker.dart handling of multitests

tests/isolate/compile_time_error_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.
 
 // Dart test program for testing that errors thrown from isolates are
 // processed correctly and don't result in crashes.
 
 library Isolate3NegativeTest;
 import 'dart:isolate';
 import 'dart:async';
 import "package:async_helper/async_helper.dart";
 
 class TestClass {
   TestClass.named(num this.fld1)
     // Should cause a compilation error (for the spawned isolate). It is a
     // runtime error for the test.
-    : fld2 = this.fld1 // /// 01: compile-time error
+    : fld2 = this.fld1 // //# 01: compile-time error
   ;
   num fld1;
   num fld2;
 }
 
 void entry(SendPort replyTo) {
   var tmp = new TestClass.named(10);
   replyTo.send("done");
 }
 
 main() {
   asyncStart();
   ReceivePort response = new ReceivePort();
   Isolate.spawn(entry, response.sendPort);
   response.first.then((_) {
     asyncEnd();
   });
 }