Add topic_last_poster_id and topic_last_post_time to Event core.modify_posting_auth

It would be useful to add additional info from the sql queries to the event data.

For example, adding topic_last_poster_id and topic_last_post_time would remove one query here.

The data has already been fetched from the database (in the $post_data array), but not passed on to the event.

I would suggest passing the post_data array to the event, since the contents change depending on the mode and other data will be useful for other extensions.