unittest step2: bye bye to multiple entrypoints for unittest

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('dart:isolate');
+#import('unittest.dart');
 
-#source('config.dart');
-#source('shared.dart');
-
-class PlatformConfiguration extends Configuration {
+class VmConfiguration extends Configuration {
   void onDone(int passed, int failed, int errors, List<TestCase> results) {
     try {
       super.onDone(passed, failed, errors, results);
     } catch (Exception ex) {
       // A non-zero exit code is used by the test infrastructure to detect
       // failure.
       exit(1);
     }
   }
 }
+
+void useVmConfiguration() {
+  configure(new VmConfiguration());
+}