Move unittest from lib to pkg.

tests/html/xhr_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.
 
 #library('XHRTest');
-#import('../../lib/unittest/unittest.dart');
-#import('../../lib/unittest/html_config.dart');
+#import('../../pkg/unittest/unittest.dart');
+#import('../../pkg/unittest/html_config.dart');
 #import('dart:html');
 
 main() {
   useHtmlConfiguration();
 
   print(window.location.href);
   test('XHR', () {
     XMLHttpRequest xhr = new XMLHttpRequest();
     xhr.open("GET", "NonExistingFile", true);
     xhr.on.readyStateChange.add(expectAsync1((event) {
         if (xhr.readyState == 4) {
           Expect.equals(0, xhr.status);
           Expect.stringEquals('', xhr.responseText);
         }
       }));
     xhr.send();
   });
 
   test('XHR.get', () {
       new XMLHttpRequest.get("NonExistingFile", expectAsync1((xhr) {
           Expect.equals(XMLHttpRequest.DONE, xhr.readyState);
           Expect.equals(0, xhr.status);
           Expect.stringEquals('', xhr.responseText);
       }));
   });
 }