Prohibit use of dynamic when extending or implementing classes (was crashing).

tests/language/dynamic2_test.dart

Index: tests/language/dynamic2_test.dart
===================================================================
--- tests/language/dynamic2_test.dart	(revision 0)
+++ tests/language/dynamic2_test.dart	(revision 0)
@@ -0,0 +1,15 @@
+// Copyright (c) 2013, 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.
+//
+// Test the prohibited use of 'dynamic' in extending and implementing classes.
+
+class A
+  extends dynamic  /// 00: compile-time error
+  implements dynamic  /// 01: compile-time error
+{
+}
+
+main() {
+  new A();
+}