UpdateBridgesFromAuthority isn't actually usable

Thanks to the bug #1938 (closed) fix, UpdateBridgesFromAuthority only works if you can build a circuit to the authority. But if you're using bridges, you can't connect to the authority without bridges, so setting UpdateBridgesFromAuthority 1 is still not going to be a great idea unless you already have a bridge descriptor somehow.

What we should really do (according to comments on #1938 (closed) , which I agree with) is implement behavior where we can try the authority or try asking the bridges we know, falling back from one to the other intelligently.