allow directory authorities to badexit by country code

Now that we have many thousands of users in Syria, some dozen of them click 'share' each day.

There's a broader discussion to be had here around whether these are useful relays for the Tor network at all (generally the relays we have there are short-lived and trivial-capacity, so maybe it doesn't matter so much), but I don't think we want to subject our users in the 'free' countries (whatever those are) to Bluecoat's filters.

I was going to go make a few hundred authdirbadexit lines when I realized that the authorities already have a geoip db built-in and they could just do the lookup themselves.

I marked 'minor' priority since whether we actually want to deploy the feature probably wants more discussion.