Add async initialization for Intl.message and an example

pkg/intl/example/basic/messages_de_de.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_de_DE');
+#import('../../intl.dart');
+
+runAt(time, day) => Intl.message('Ausgedruckt am $time am $day.', name: 'runAt',
+    args: [time, day]);