Some documentation added.

(stty_init): Change default value to False instead of None.
(__use): New function.
(_inherit_stty): New function.
(_stty_init): New function.
(_spawn): New arguments: inherit_stty, stty_init.  Only inherit
	stty settings if stdin is a tty.  If an exception occurs in
	the child, transfer it to the parent as a
	remote_exception.Remote object.
(Spawn.__init__): New optional arguments: inherit_stty, stty_init.
(spawn2): Pass all arguments to the Spawn constructor.