Implement 'SocksPort auto' and 'ControlPort auto'

In order to ship Tor Browser Bundles that do not conflict with distribution-installed tor clients and tor relays, we must give TBB the ability to automatically choose a new SOCKS port and Control port if the default ports are in use. (See #2264 (closed)).

This requires a few pieces to coordinate. Creating torrc options to allow tor to listen on automatically free ports is the first step.

These options also need to kick out a log line at notice level that Vidalia is capable of easily parsing (#3077 (closed)).

I think we need to do this ASAP, and that it should go into 0.2.2.x, so we can release TBBs that don't break when people have another tor installed. I can code this myself it that is what it takes (but obviously I'd prefer not to :).