(class client_x11_display): Inherit client_x11_handler.
(channel_open_x11): Invoke the handler's open method.
(client_add_x11_handler): Take an argument of type
client_x11_handler *, not resource *.
(do_client_x11_display_open): New function.
(make_client_x11_display): New argument single_connection.
Initialize super class and open method.
(do_action_x11_success): Updated for client_x11_display inheriting
client_x11_handler.
(make_x11_action): New argument single_connection.

Rev: src/client_x11.c:1.33