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

test/codegen/syncstar_yield_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";
-
-Iterable<int> foo1() sync* {
-  yield 1;
-}
-
-Iterable<int> foo2(p) sync* {
-  bool t = false;
-  yield null;
-  while (true) {
-    a: for (int i = 0; i < p; i++) {
-      if (!t) {
-        for (int j = 0; j < 3; j++) {
-          yield -1;
-          t = true;
-          break a;
-        }
-      }
-      yield i;
-    }
-  }
-}
-
-// p is copied to all Iterators from the Iterable returned by foo3.
-// Also each iterator will have its own i.
-Iterable<int> foo3(int p) sync* {
-  int i = 0;
-  i++;
-  p++;
-  yield p + i;
-}
-
-main() {
-  Expect.listEquals([1], foo1().toList());
-  Expect.listEquals([null, -1, 0, 1, 2, 3, 0, 1, 2, 3],
-      foo2(4).take(10).toList());
-  Iterable t = foo3(0);
-  Iterator it1 = t.iterator;
-  Iterator it2 = t.iterator; /// copyParameters: ok
-  it1.moveNext();
-  it2.moveNext(); /// copyParameters: continued
-  Expect.equals(2, it1.current);
-  // TODO(sigurdm): Check up on the spec here.
-  Expect.equals(2, it2.current);  /// copyParameters: continued
-  Expect.isFalse(it1.moveNext());
-  // Test that two `moveNext()` calls are fine.
-  Expect.isFalse(it1.moveNext());
-  Expect.isFalse(it2.moveNext()); /// copyParameters: continued
-  Expect.isFalse(it2.moveNext()); /// copyParameters: continued
-}