fix bug with registerException

lib/src/internal_test_case.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.
 
 library unittest.internal_test_case;
 
 import 'dart:async';
 
 import '../unittest.dart';
 import 'test_environment.dart';
@@ skipping 176 matching lines @@
   /// Marks the test as having passed.
   void pass() {
     _complete(PASS);
   }
 
   void registerException(error, [StackTrace stackTrace]) {
     var message = error is TestFailure ? error.message : 'Caught $error';
     if (result == null) {
       fail(message, stackTrace);
     } else {
-      error(message, stackTrace);
+      this.error(message, stackTrace);
     }
   }
 
   /// Marks the test as having failed.
   void fail(String messageText, [StackTrace stack]) {
     if (result != null) {
       var newMessage = result == PASS
           ? 'Test failed after initially passing: $messageText'
           : 'Test failed more than once: $messageText';
       // TODO(gram): Should we combine the stack with the old one?
@@ skipping 10 matching lines @@
 
   /// Indicates that an asynchronous callback has completed, and marks the test
   /// as passing if all outstanding callbacks are complete.
   void markCallbackComplete() {
     callbackFunctionsOutstanding--;
     if (callbackFunctionsOutstanding == 0 && !isComplete) pass();
   }
 
   String toString() => result != null ? "$description: $result" : description;
 }