allow users to change the address that their notifications go to

Currently when a user clicks the link to unsubscribe it just does it and that's it.

It would be nice if
1. they got a confirmation form
2. the form also let them change the e-mail address that it's going to

Item #2 is a little tricky. We can't let people do it for that e-mail across the whole site, otherwise an anonymous user could change the notification settings for someone on dozens of comments. So, we'd have to do it per notification which is easy enough technically but not very fun from a usability perspective.