Fix negative test by not complicating it by using the unit test framework.

tests/isolate/isolate2_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 exceptions in other isolates bring down
 // the program.
 
 #library('Isolate2NegativeTest');
 #import('dart:isolate');
-#import('../../lib/unittest/unittest.dart');
 
 void entry() {
   throw "foo";
 }
 
 main() {
-  test("catch exception from other isolate", () {
-    spawnFunction(entry);
-  });
+  SendPort port = spawnFunction(entry);
 }