tor-parallel-relay-conn/changes/prop297

  o Minor features (required protocols):
    - Tor no longer exits if it is missing a required protocol, if the
      consensus that requires the protocol predates the release date of the
      version of Tor. This change prevents Tor releases from exiting because
      of an old cached consensus, on the theory that a newer cached
      consensus might not require the protocol.  Implements proposal 297;
      closes ticket 27735.