Make scrollbar structures into lisp objects, so that they can be

Make scrollbar structures into lisp objects, so that they can be
	GC'd; this allows windows and scrollbars can refer to each other
	without worrying about dangling pointers.
	* xterm.h (struct x_display): vertical_scrollbars and
	judge_timestamp members deleted.
	(struct scrollbar): Redesigned to be a template for a Lisp_Vector.
	(SCROLLBAR_VEC_SIZE, XSCROLLBAR, SCROLLBAR_PACK, SCROLLBAR_UNPACK,
	SCROLLBAR_X_WINDOW, SET_SCROLLBAR_X_WINDOW,
	VERTICAL_SCROLLBAR_INSIDE_WIDTH, VERTICAL_SCROLLBAR_TOP_RANGE,
	VERTICAL_SCROLLBAR_INSIDE_HEIGHT, VERTICAL_SCROLLBAR_MIN_HANDLE):
	New macros, to help deal with the lispy structures, and deal with
	the graphics.
	* frame.h (WINDOW_VERTICAL_SCROLLBAR): Macro deleted.
	(struct frame): New fields `scrollbars' and
	`condemned_scrollbars', for use by the scrollbar implementation.
	[MULTI_FRAME and not MULTI_FRAME] (FRAME_SCROLLBARS,
	FRAME_CONDEMNED_SCROLLBARS): Accessors for the new field.
	* window.h (struct window): Doc fix for vertical_scrollbar field.
	* frame.c (make_frame): Initialize the `scrollbars' and
	`condemned_scrollbars' fields of the new frame.
	* alloc.c (mark_object): Mark the `scrollbars' and
	`condemned_scrollbars' slots of frames.
	* xterm.c (x_window_to_scrollbar): Scrollbars are chained on
	frames' scrollbar field, not their x.display->vertical_scrollbars
	field.
	(x_scrollbar_create, x_scrollbar_set_handle, x_scrollbar_move,
	x_scrollbar_remove, XTset_vertical_scrollbar,
	XTcondemn_scrollbars, XTredeem_scrollbar, XTjudge_scrollbars,
	x_scrollbar_expose, x_scrollbar_handle_click,
	x_scrollbar_handle_motion): Substantially rewritten to correct
	typos and brainos, and to accomodate the lispy structures.