* window.c (window_internal_width): New function.

* window.c (window_internal_width): New function.
	* lisp.h (window_internal_height, window_internal_width): Add
	extern declarations for these.
	* dispnew.c (direct_output_for_insert, direct_output_forward_char,
	buffer_posn_from_coords): Use window_internal_width instead of
	writing out its definition.
	* indent.c (compute_motion): Doc fix; mention scrollbars and
	window_internal_width.
	(pos_tab_offset, Fvertical_motion): Use window_internal_width
	instead of writing it out.
	* window.c (Fpos_visible_in_window_p, Fwindow_width, Fscroll_left,
	Fscroll_right): Same.
	* xdisp.c (redisplay, try_window, try_window_id,
	display_text_line): Same.