tor_circmgr::usage: Allow requesting a circuit that supports "exiting to some unspecified port"
The RESOLVE command is only supported by Exit relays, so we want to deliver it only on circuits that support a nonempty exit policy. But right now we don't have support in
tor_circmgr::usage for asking for "any exit that supports at least one port"; we can can only ask for specific ports.
Once this is done we can fix the kludge in