Update unittest to new package layout.

tests/isolate/request_reply_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("RequestReplyTest");
 
 #import("dart:isolate");
-#import('../../pkg/unittest/unittest.dart');
+#import('../../pkg/unittest/lib/unittest.dart');
 
 void entry() {
   port.receive((message, SendPort replyTo) {
     replyTo.send(message + 87);
     port.close();
   });
 }
 
 void main() {
   test("call", () {
     SendPort port = spawnFunction(entry);
     port.call(42).then(expectAsync1((message) {
       Expect.equals(42 + 87, message);
     }));
   });
 
   test("send", () {
     SendPort port = spawnFunction(entry);
     ReceivePort reply = new ReceivePort();
     port.send(99, reply.toSendPort());
     reply.receive(expectAsync2((message, replyTo) {
       Expect.equals(99 + 87, message);
       reply.close();
     }));
   });
 }