Update unittest to new package layout.

tests/isolate/nested_spawn_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.
 
 // Dart test program for testing that isolates can spawn other isolates.
 
 #library('NestedSpawnTest');
 #import("dart:isolate");
-#import('../../pkg/unittest/unittest.dart');
+#import('../../pkg/unittest/lib/unittest.dart');
 
 void isolateA() {
   port.receive((msg, replyTo) {
     Expect.equals("launch nested!", msg);
     SendPort p = spawnFunction(isolateB);
     p.call("alive?").then((msg) {
       Expect.equals("and kicking", msg);
       replyTo.send(499, null);
       port.close();
     });
@@ skipping 10 matching lines @@
 
 
 main() {
   test("spawned isolates can spawn nested isolates", () {
     SendPort port = spawnFunction(isolateA);
     port.call("launch nested!").then(expectAsync1((msg) {
       Expect.equals(499, msg);
     }));
   });
 }