drupal 7 comment moderation modules
You should be able to "set different statuses for comments, like approved, pending, spam and unapproved" using Flags, which are D7 only.

I could not find anything that adds revisions to comments, or comments to flag changes.

The workflow module allows you to assign states to nodes, and comment each state change, but the comment_workflow module is available only for D5. Hopefully someone else might have better news.