Update unittest to new package layout.

tests/isolate/unresolved_ports_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.
 
 // spawns multiple isolates and sends unresolved ports between them.
 #library('unresolved_ports');
 #import('dart:isolate');
-#import('../../pkg/unittest/unittest.dart');
+#import('../../pkg/unittest/lib/unittest.dart');
 
 // This test does the following:
 //  - main spawns two isolates: 'tim' and 'beth'
 //  - 'tim' spawns an isolate: 'bob'
 //  - main starts a message chain:
 //       main -> beth -> tim -> bob -> main
 //    by giving 'beth' a send-port to 'tim'.
 
 bethIsolate() {
   port.receive((msg, reply) => msg[1].send(
@@ skipping 25 matching lines @@
     SendPort tim = spawnFunction(timIsolate);
     SendPort beth = spawnFunction(bethIsolate);
 
     beth.send(
         // because tim is created asynchronously, here we are sending an
         // unresolved port:
         ['main says: Beth, find out if Tim is coming.', tim],
         port.toSendPort());
   });
 }