Move unittest tests underneath it in /pkg

tests/lib/unittest/mock_stepwise_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('../../../pkg/unittest/unittest.dart');
-
-main() {
-  test('Mocking: stepwiseValidate', () {
-    LogEntryList logList = new LogEntryList('test');
-    for (var i = 0; i < 10; i++) {
-      LogEntry e = new LogEntry(null, 'foo', [i], Action.IGNORE);
-      logList.add(e);
-    }
-    int total = 0;
-    logList.stepwiseValidate((log, pos) {
-        return 0;
-    });
-  });
-}