http://i3xi5qxvbrngh3g6o7czwjfxwjzigook7zxzjmgwg5b7xnjcn5hzciad.onion/proposals/125-bridges.html
The theory is that either the bridge is available now, in which
case you can get a fresh descriptor, or it's not, in which case an
old descriptor won't do you much good.
We could disable writing out the bridge lines to the state file, if
we think this is a problem.