Add async initialization for Intl.message and an example

pkg/intl/example/basic/messages_th_th.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.
+
+/**
+ * This is a library that provides messages for a German locale. All the
+ * messages from the main program should be duplicated here with the same
+ * function name.  Note that the library name is significant, as it's looked
+ * up based on a naming convention.
+ */
+
+#library('messages_th_TH');
+#import('../../intl.dart');
+
+runAt(time, day) =>
+    Intl.message('วิ่ง $time on $day.', name: 'runAt', args: [time, day]);
+