Fix warnings_checker.dart handling of multitests

tests/compiler/dart2js_extra/mirror_printer_test.dart

 // Copyright (c) 2013, 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.
 
 /// Prints all information about all mirrors. This tests that it is possible to
 /// enumerate all reflective information without crashing.
 
 // Note: Adding imports below is fine for regression tests. For example,
 // 'crash_library_metadata.dart' is imported to ensure the compiler doesn't
 // crash.
 
 // TODO(ahe): This test should be extended until we are sure all data is
 // printed.
 
 library test.mirror_printer_test;
 
 @MirrorsUsed(targets: '*')
 import 'dart:mirrors';
 
 import 'crash_library_metadata.dart'; // This would crash dart2js.
 
 // Importing dart:html to make things interesting.
-import 'dart:html'; /// 01: ok
+import 'dart:html'; //# 01: ok
 
 class MirrorPrinter {
   final StringBuffer buffer;
   final TypeMirror dynamicType = currentMirrorSystem().dynamicType;
 
   int indentationLevel = 0;
 
   MirrorPrinter(this.buffer);
 
   void w(object) {
@@ skipping 144 matching lines @@
     StringBuffer buffer = new StringBuffer();
     libraries.values.forEach(new MirrorPrinter(buffer).writeLibrary);
     return buffer;
   }
 }
 
 main() {
   print(MirrorPrinter.stringify(currentMirrorSystem().libraries));
   // Clear the nodes to avoid confusing the fine test framework (by "fine" I
   // mean something else) -- ahe.
-  document.body.nodes.clear(); /// 01: continued
+  document.body.nodes.clear(); //# 01: continued
 }