Updates not considered in last post

Issue Summary

As currently implemented, when a page is updated, it will show in Xtracker as updated, but the date of last post is either when the page was originally created or when the last comment was posted, i.e., the last *new* post. This means that the list gives one no alert to updated pages. It would be better, at least as an option, to update the date of last post to correspond to the date of last revision.