* window.c (window_scroll_pixel_based_preserve_x)

* window.c (window_scroll_pixel_based_preserve_x)
(window_scroll_preserve_hpos, window_scroll_preserve_vpos): New vars.
(window_scroll_pixel_based, window_scroll_line_based):
Use them to preserve column positions.
(syms_of_window): Initialize them.
* indent.c (Fvertical_motion): Extend first arg to allow passing an
(HPOS . VPOS) pair.
* xdisp.c (move_it_in_display_line_to): Improve the type of its args.
(move_it_in_display_line): New wrapper.
* dispextern.h (move_it_in_display_line): Declare.