[hgreview] Associate issue numbers with revisions

[trev]

Background

Currently, you have to specify -i explicitly when updating a review. This doesn't seem necessary if the review was created via hgreview.

What to change

Create a local tag like issue-1234 and associate it with the revision uploaded, for revision ranges with the last revision uploaded. On update, look for such tags within the revision range and set the issue number automatically (move the tag up if necessary).

We'll need some way to override this behavior in case a new review needs to be created. This can be a --new parameter, existing tags in the revision range should be replaced then (new review takes precedence over the old and possibly removed one).