Directory authorities should reject relays with #20499 bug
Once we resolve legacy/trac#20499 (moved), or more precisely, once we figure out which versions it affects, we should teach the directory authorities to withhold the Guard flag from relays that are running those versions.
Right now you can't bootstrap from e.g. sofia, which is a huge guard running 0.2.9.3-alpha.
Then later -- or maybe this will turn out to be the easiest solution for everything -- we can teach the directory authorities to simply reject descriptors from relays running these buggy versions.
[I'm not sure which milestone to put this in, since it will need to get into a majority of directory authorities for it to matter. :/ ]