Subscribers are notified twice for new posts

Whenever a new post is written, subscribers get two email notifications instead of one.

The reason for this is that the model is saved twice during processing in AddPostView.

The attached patch does not remove the double save (because it is a little complicated to do so, and may have other side effects), but rather notifies users only when "created" arg of post_save signal is True - I don't think it is intended to send email when someone just edits an existing post anyway.