Move unittest from lib to pkg.

tests/isolate/mandel_isolate_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('MandelIsolateTest');
 #import('dart:isolate');
-#import('../../lib/unittest/unittest.dart');
+#import('../../pkg/unittest/unittest.dart');
 
 final TERMINATION_MESSAGE = -1;
 final N = 100;
 final ISOLATES = 20;
 
 main() {
   test("Render Mandelbrot in parallel", () {
     final state = new MandelbrotState();
     state._validated.future.then(expectAsync1((result) {
       expect(result, isTrue);
@@ skipping 114 matching lines @@
 void processLines() {
   port.receive((message, SendPort replyTo) {
     if (message == TERMINATION_MESSAGE) {
       assert(replyTo == null);
       port.close();
     } else {
       replyTo.send(processLine(message), null);
     }
   });
 }