Update unittest to new package layout.

tests/isolate/nested_spawn2_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 and
 // that the nested isolates can communicate with the main once the spawner has
 // disappeared.
 
 #library('NestedSpawn2Test');
 #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.send(replyTo, null);
     port.close();
   });
 }
 
@@ skipping 42 matching lines @@
         _call(replyTo, msg3, expectAsync2((msg, replyTo) {
           Expect.equals("4", msg[0]);
           _call(replyTo, msg5, expectAsync2((msg, replyTo) {
             Expect.equals("6", msg[0]);
           }));
         }));
       }));
     }));
   });
 }