Fix warnings_checker.dart handling of multitests

tests/language_strong/abstract_syntax_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.
 
 import "package:expect/expect.dart";
 
 main() {
   var b = new B();
   Expect.equals(42, b.foo());
 }
 
 class A {
-  foo(); // /// 00: static type warning
-  static bar(); // /// 01: compile-time error
+  foo(); // //# 00: static type warning
+  static bar(); // //# 01: compile-time error
 }
 
 class B extends A {
   foo() => 42;
   bar() => 87;
 }