docs: def destinations(self):
          """
          Provides a list of destinations (queue "addresses") available.
  
          @return: A list of the detinations available.
          @rtype: C{set}
          """
          session = meta.Session()
          sel = select([distinct(model.frames_table.c.destination)])
          result = session.execute(sel)
          return set([r[0] for r in result.fetchall()])