o Major bugfixes:
    - Detect 'ORPort 0' as meaning, uniformly, that we're not running
      as a server. Previously, some of our code would treat the
      presence of any ORPort line as meaning that we should act like a
      server, even though our new listener code would correctly not
      open any ORPorts for ORPort 0. Similar bugs in other Port
      options are also fixed. Fixes bug 6507; bugfix on 0.2.3.3-alpha.