Bug cleanup: add comment about unspecified behavior if the object

lib/core/iterator.dart

Index: lib/core/iterator.dart
diff --git a/lib/core/iterator.dart b/lib/core/iterator.dart
index 14043754528178ff75d1bdd680c6375b34c9e0df..c3a346d87ce904ae3defb32e285e2c525bfa47e4 100644
--- a/lib/core/iterator.dart
+++ b/lib/core/iterator.dart
@@ -1,4 +1,4 @@
-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// 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.
 
@@ -6,6 +6,9 @@
  * The [Iterator] class provides methods to iterate over an object. It
  * is transparently used by the for-in construct to test for the end
  * of the iteration, and to get the elements.
+ *
+ * If the object iterated over is changed during the iteration, the
+ * behavior is unspecified.
  */
 abstract class Iterator<E> {
   /**