CannotListenError case of reactor.listenTCP leaks a socket for the garbage collector to clean up

[exarkun]

The socket is created but not closed in the case of an exception:

    def startListening(self):
        """Create and bind my socket, and begin listening on it.                                                                                                                                  
                                                                                                                                                                                                  
        This is called on unserialization, and must be called after creating a                                                                                                                    
        server to begin listening on the specified port.                                                                                                                                          
        """
        if self._preexistingSocket is None:
            # Create a new socket and make it listen                                                                                                                                              
            try:
                skt = self.createInternetSocket()
                if self.addressFamily == socket.AF_INET6:
                    addr = _resolveIPv6(self.interface, self.port)
                else:
                    addr = (self.interface, self.port)
                skt.bind(addr)
            except socket.error as le:
                raise CannotListenError(self.interface, self.port, le)
            skt.listen(self.backlog)