Use correct message type when sending last published PEP/PubSub items

When sending last published PubSub items, set the message type that [was used for broadcasting][1] those items originally.  For example, PEP messages will have [`type='headline'`][2] specified when published, so that type should also be used when resending those messages.

[1]: https://github.com/processone/ejabberd/blob/cc958f7787a824f9d541a05fdbd37f4c3047ee7d/src/mod_pubsub.erl#L4485
[2]: http://xmpp.org/extensions/xep-0060.html#impl-offline