Fix warnings_checker.dart handling of multitests

tests/language/dynamic_prefix_core_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.
 // Test explicit import of dart:core in the source code..
 
 library DynamicPrefixCoreTest.dart;
 import "package:expect/expect.dart";
 import "dart:core" as mycore;
 
 void main() {
   // Should still be available because it is not a member of dart:core.
   Expect.isTrue(dynamic is mycore.Type);
 
-  Expect.throws(() => mycore.dynamic is mycore.Type, //    /// 01: static type warning
-                (e) => e is mycore.NoSuchMethodError, //   /// 01: continued
-                'dynamic is not a member of dart:core'); /// 01: continued
+  Expect.throws(() => mycore.dynamic is mycore.Type, //    //# 01: static type warning
+                (e) => e is mycore.NoSuchMethodError, //   //# 01: continued
+                'dynamic is not a member of dart:core'); //# 01: continued
 }