def close_circuit(circuit):
    """
        Asks Tor to close the circuit. Note that the Circuit instance
        is only removed as a result of the next CIRC CLOSED event. The
        Deferred returned from this method callbacks when the
        CLOSECIRCUIT command has successfully executed, not when the
        circuit is actually gone.

        If you wish to know when this circuit is actually gone, add an
        ICircuitListener and wait for circuit_closed()
        """
