Move unittest from lib to pkg.

tests/lib/unittest/mock_regexp_negative_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('unittestTest');
-#import('../../../lib/unittest/unittest.dart');
+#import('../../../pkg/unittest/unittest.dart');
 
 main() {
   test('Mocking: RegExp CallMatcher bad', () {
     var m = new Mock();           
     m.when(callsTo(matches('^[A-Z]'))).          
            alwaysThrow('Method names must start with lower case.');      
     m.Test();         
   });
 }