o Minor features:
    - When any country code is listed in ExcludeNodes or
      ExcludeExitNodes, and we have GeoIP information, also exclude
      all nodes with unknown countries ({??} and {A1} if
      present). This behavior is controlled by the new
      GeoIPExcludeUnknown option: you can make such nodes always
      excluded with 'GeoIPExcludeUnknown 1', and disable the feature
      with 'GeoIPExcludeUnknown 0'. Setting 'GeoIPExcludeUnknown auto'
      gets you the default behavior.  Implements feature 7706.