Support for type dynamic in VM

tests/language/import_core_prefix_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.
 // Test explicit import of dart:core in the source code..
 
 #library("ImportCorePrefixTest.dart");
 #import("dart:core", prefix:"mycore");
 
 void main() {
   var test = new mycore.Map<mycore.int,mycore.String>();
   mycore.bool boolval = false;
   mycore.int variable = 10;
   mycore.num value = 10;
-  mycore.Dynamic d = null;
+  mycore.dynamic d = null;
 }