tor-error: Introduce ErrorKind::AlreadyRunning
Our HSS code isn't going to work if you run more than one copy. Soon we'll detect this (via our use of tor_persist).
There may be other places this ought to be used. Eg if we get EADDRINUSE from trying to set up a proxy, maybe ...
CC @nickm @gabi-250 since I'd like buy-in from both of you that this new ErrorKind is appropriate. I was surprised not to find it, so maybe I am missing something or confused.