Added support for exports and re-exports.

tests/language/export_cyclic_helper2.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.
 
-class A {
+library export_cyclic_helper2;
+
+import 'export_cyclic_test.dart';
+import 'export_cyclic_helper3.dart';
+export 'export_cyclic_test.dart';
+export 'export_cyclic_helper3.dart';
+
+class C {
   A a;
-
-  bar(c) {
-    c.a = 2; /// 01: dynamic type error
-  }
+  B b;
+  C c;
+  D d;
 }
-
-class B {
-  int a;
-}
-
-main() {
-  new A().bar(new A()); /// 01: continued
-  new A().bar(new B());
-}