why doesn't MemoryServer.tearDown deregister it?

[Martin Pool]

We have

class MemoryServer(Server):
    """Server for the MemoryTransport for testing with."""

    def setUp(self):
        """See bzrlib.transport.Server.setUp."""
        self._dirs = {'/':None}
        self._files = {}
        self._locks = {}
        self._scheme = "memory+%s:///" % id(self)
        def memory_factory(url):
            result = MemoryTransport(url)
            result._dirs = self._dirs
            result._files = self._files
            result._locks = self._locks
            return result
        register_transport(self._scheme, memory_factory)

    def tearDown(self):
        """See bzrlib.transport.Server.tearDown."""
        # unregister this server


why doesn't the tearDown actually deregister it, as it promises to?
It seems like that would free some memory.  Can we at least add an
explanatory comment?

-- 
Martin <http://launchpad.net/~mbp/>