Reload keypins on SIGHUP? Or provide some other way to undo a single keypin?

Right now, there isn't a way to undo a buggy key-pin without stopping the authority, editing the keypin file, and restarting it. Not good: authority operators shouldn't have to reboot just because we had a bug.

We should fix this before we release 0.2.7.2-alpha.

I see two four six options here.

1. Make it okay to edit the key-pinning journal on a running Tor. That's not so great; we need to be able to append to it, and editors may have swap-file races with it.
2. Add a torrc option to unpin an existing key. This would only need to be stuck into the torrc once; it would remove the pin, and allow a new key pin to occur.
3. No fix; hope that this situation never happens again; tell the authoritiy ops to edit the keypinning file when they upgrade, or give them a script to do it.
4. One-off fix: undo the pin in software for the two specific keypairs affected, and hope this never happens again.
5. As 3, but tell the ops to remove the file.
6. As 5, but have Tor use a new file name, and remove the old one it exists, so that the ops don't have to do anything at all.