Move unittest from lib to pkg.

lib/unittest/vm_config.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.
-
-/**
- * A simple unit test library for running tests on the VM.
- */
-#library('unittest');
-
-#import('dart:io');
-#import('unittest.dart');
-
-class VmConfiguration extends Configuration {
-  void onDone(int passed, int failed, int errors, List<TestCase> results,
-      String uncaughtError) {
-    try {
-      super.onDone(passed, failed, errors, results, uncaughtError);
-    } catch (Exception ex) {
-      // A non-zero exit code is used by the test infrastructure to detect
-      // failure.
-      exit(1);
-    }
-  }
-}
-
-void useVmConfiguration() {
-  configure(new VmConfiguration());
-}