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

test/codegen/language/async_break_in_finally_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.
+
+import "package:expect/expect.dart";
+import "package:async_helper/async_helper.dart";
+
+then43() async {
+  label: try {
+    return await 42;
+  } finally {
+    break label;
+  }
+  return await 43;
+}
+
+then42() async {
+  label: try {
+    return await 42;
+  } finally {
+  }
+  return await 43;
+}
+
+now43() {
+  label: try {
+    return 42;
+  } finally {
+    break label;
+  }
+  return 43;
+}
+
+now42() {
+  label: try {
+    return 42;
+  } finally {
+  }
+  return 43;
+}
+
+test() async {
+  Expect.equals(42, await then42());
+  Expect.equals(43, await then43());
+  Expect.equals(42, now42());
+  Expect.equals(43, now43());
+}
+
+main() {
+  asyncStart();
+  test().then((_) => asyncEnd());
+}