* window.c: Try to deal coherently with deleted windows:

* window.c: Try to deal coherently with deleted windows:
*	(Flive_window_p): New function.
	(Qlive_window_p): New variable, to name it in type errors.
	(syms_of_window): Defsubr Slive_window_p, init and staticpro
	Qlive_window_p.
	(decode_window): Use CHECK_LIVE_WINDOW instead of
	CHECK_WINDOW; the only thing a user should be able to do to a dead
	window is check its type.
	(Fcoordinates_in_window_p, Fnext_window, Fprevious_window,
	Fdelete_other_windows, Fselect_window, Fsplit_window,
	Fscroll_other_window): Use CHECK_LIVE_WINDOW instead of
	CHECK_WINDOW.
	(Fdelete_window): If WINDOW is a deleted window, do nothing;
	there's no harm in allowing people to delete deleted windows.
	Delete all of WINDOW's subwindows, too.
	(delete_all_subwindows): Set the buffer, vchild, and hchild of the
	windows we delete all to nil.

	* window.c (Fwindow_minibuffer_p): Make the WINDOW argument
	optional, like all the other window-querying functions.

	* window.c (Fpos_visible_in_window_p): Use decode_window to handle
	the WINDOW argument, instead of writing out that function's code.

	* window.c (check_frame_size): Don't define this extern; that
	doesn't mean anything.

	* window.c (Fdelete_window): Choose an alternative when we delete
	any frame's selected window, not just when we delete the selected
	frame's selected window.