There are a few reasons that relays might be uploading desciptors
without saying X-Desc-Gen-Reason:
  1. They are running an old version of our software, before 0.3.2.stable.
  2. They are not running our software, but they are claiming they
     are.
  3. They are uploading through a proxy that strips X-Desc-Gen-Reason.
  4. They somehow had a bug in their software.

According to the 25686 data, 1 is the most common reason.  This
ticket is an attempt to diagnose case 4, or prove that case 4
doesn't actually happen.