Update unittest to new package layout.

tests/isolate/count_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("CountTest");
 #import('dart:isolate');
-#import('../../pkg/unittest/unittest.dart');
+#import('../../pkg/unittest/lib/unittest.dart');
 
 void countMessages() {
   int count = 0;
   port.receive((int message, SendPort replyTo) {
     if (message == -1) {
       Expect.equals(10, count);
       replyTo.send(-1, null);
       port.close();
       return;
     }
@@ skipping 19 matching lines @@
 
       Expect.equals((count - 1) * 2, message);
       remote.send(count++, reply);
       if (count == 10) {
         remote.send(-1, reply);
       }
     }, count: 11));
     remote.send(count++, reply);
   });
 }