DocTor should understand the shared randomness protocol

There are a few partioning attacks on the shared randomness protocol (#16943 (moved)) that are not easy to fix. The attacks are not that dangerous and they are quite detectable. It would be nice if DocTor could catch them.

Some detection ideas can be found in this mail: https://lists.torproject.org/pipermail/tor-dev/2015-September/009460.html

Thanks!