Move unittest from lib to pkg.

tests/isolate/isolate3_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.
 
 // Dart test program for testing that errors thrown from isolates are
 // processed correctly and don't result in crashes.
 
 #library('Isolate3NegativeTest');
 #import('dart:isolate');
-#import('../../lib/unittest/unittest.dart');
+#import('../../pkg/unittest/unittest.dart');
 
 class TestClass {
   TestClass.named(num this.fld1) : fld2=fld1 {
     TestClass.i = 0;  // Should cause a compilation error.
   }
   num fld1;
   num fld2;
 }
 
 void entry() {
   port.receive((ignored, replyTo) {
     var tmp = new TestClass.named(10);
     replyTo.send(tmp, null);
   });
 }
 
 main() {
   test("child isolate compilation errors propagate correctly. ", () {
     void msg_callback(var message) {
       // This test is a negative test and should not complete successfully.
     }
     SendPort port = spawnFunction(entry);
     port.call("foo").then(expectAsync1(msg_callback));
   });
 }