Update unittest to new package layout.

tests/isolate/unresolved_ports_negative_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.
 
 // negative test to ensure that API_unresolvedPortsTest works.
 #library('unresolved_ports');
 #import('dart:isolate');
-#import('../../pkg/unittest/unittest.dart');
+#import('../../pkg/unittest/lib/unittest.dart');
 
 bethIsolate() {
   port.receive(expectAsync2((msg, reply) => msg[1].send(
         '${msg[0]}\nBeth says: Tim are you coming? And Bob?', reply)));
 }
 
 timIsolate() {
   SendPort bob = spawnFunction(bobIsolate);
   port.receive(expectAsync2((msg, reply) => bob.send(
         '$msg\nTim says: Can you tell "main" that we are all coming?', reply)));
@@ skipping 19 matching lines @@
     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());
   });
 }