When unsubscribing someone, the unsubscribee should be notified

[Matt Zimmerman]

See for example bug #52617, where ubuntu-security was unsubscribed, but no mail was sent to the team contact address. There are multiple members of the team, and it helps to be notified that someone has already unsubscribed the team, so that the other team members realize this when reading the thread and don't duplicate the effort.

I think this has to do with the mail digesting functionality, since the team is already unsubscribed when the comment mail is sent out. However, on the other hand, I appreciate it when I add a comment, then remember to subscribe someone, and they get the mail, so maybe this cuts both ways...