UpdateBridgesFromAuthority dangerous
Now that we've fixed #1138 (moved), it might be tempting to start distributing identity fingerprints along with our bridge addresses again, so clients can try the bridge authority for the descriptor.
In retrospect, though, the plan of "first go to the centralized place that is easily associated with being a Tor bridge user, then if it's unreachable go directly to the bridge for its descriptor" is unwise.
In practice we should go to our bridges directly for their descriptor, and if we learn no descriptors, fail closed. Then, for the bridges that we've configured but didn't get a descriptor for, we can ask the bridge authority via Tor if it happens to know a newer descriptor for them.
We'll have an opportunity to make things more robust once we get going on #1852 (moved).
In the mean time, we should continue to avoid putting fingerprints on bridge addresses. (I believe Vidalia still sets UpdateBridgesFromAuthority for you when you configure a bridge.)