fixes #221, initial sync*, async, async* implementation

test/codegen/syncstar_yieldstar_test.dart

-// Copyright (c) 2015, 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.
-
-// TODO(jmesserly): this is a copy of the language test of the same name,
-// we can remove this copy when we're running against those tests.
-import "expect.dart";
-
-bar() sync* {
-  int i = 1;
-  int j = 1;
-  while (true) {
-    yield i;
-    j = i + j;
-    i = j - i;
-  }
-}
-
-foo() sync* {
-  yield* [1, 2, 3];
-  yield null;
-  // TODO(jmesserly): added cast here to work around:
-  // https://codereview.chromium.org/1213503002/
-  yield* bar() as Iterable; 
-}
-
-main () async {
-  Expect.listEquals([1, 2, 3, null, 1, 1, 2, 3, 5], foo().take(9).toList());
-}