Override node/$nid/revisions tab

Based on the feature requests/UI feedback I've been hearing, it appears more and more we need to override Drupal's default node/$nid/revisions tab. This would allow us to do things like add additional information about the revision, such as the vid, or adding a little preview snippet, or an edit link, etc.

This can be done by creating a new menu item that goes to node/$nid/revisions and declares a different callback. Because revision_moderation comes after node in the list of modules, its menu item would override node module's.

Most of the code for this would have to be copied/pasted from node_revision, node_revision_overview, etc. So it's kind of klunky in that respect. But it would work, and give us a lot more control over what was in this tab.