Move hourglass machinery to RIF.

Move hourglass machinery to RIF.
* dispextern.h (struct redisplay_interface): New members
show_hourglass and hide_hourglass.  Indent comments.
(show_hourglass, hide_hourglass): Remove prototypes.
* nsterm.m (show_hourgass, hide_hourglass): Refactor to ...
(ns_show_hourglass, ns_hide_hourglass): ... new no-ops.
(ns_redisplay_interface): Add them.
* w32fns.c (show_hourglass, hide_hourglass): Refactor to ...
* w32term.c (w32_show_hourglass, w32_hide_hourglass): ... these.
(w32_arrow_cursor): New function to hack around non-GUI frames.
(w32_redisplay_interface): Add new functions.
* w32term.h (w32_arror_cursor): Add prototype.
* xdisp.c (show_hourglass): New function, refactored out from
platform-dependend code.
(cancel_hourglass): Now call to RIF function.
* xfns.c (show_hourglass, hide_hourglass): Refactor to ...
* xterm.c (x_show_hourglass, x_hide_hourglass): ... these.
(x_redisplay_interface): Add new functions.