  o Minor feature:
    - The HSDir flag given by authorities now requires the Stable flag. For
      the current network, this results in going from 2887 to 2806 HSDirs.
      Also, it makes it harder for an attacker to launch a sybil attack by
      raising the effort for a relay to become Stable which takes at the
      very least 7 days to do so and by keeping the 96 hours uptime
      requirement for HSDir. Implements ticket #8243.
