Drop async_visible and async_iconified fields of struct frame.

Drop async_visible and async_iconified fields of struct frame.
This is possible because async input is gone; for details, see
http://lists.gnu.org/archive/html/emacs-devel/2012-12/msg00734.html.
* frame.h (struct frame): Remove async_visible and async_iconified
members, convert garbaged to unsigned bitfield.  Adjust comments.
(FRAME_SAMPLE_VISIBILITY): Remove.  Adjust all users.
(SET_FRAME_VISIBLE, SET_FRAME_ICONIFIED): New macros.
* frame.c, gtkutil.c, term.c, w32fns.c, window.c, xdisp.c:
Consistently use SET_FRAME_VISIBLE, SET_FRAME_ICONIFIED,
FRAME_VISIBLE_P and FRAME_ICONIFIED_P macros where appropriate.
* w32term.c: Ditto.
(w32_read_socket): Save iconified state to generate DEICONIFY_EVENT
properly.  Likewise for obscured.
* xterm.c: Ditto.
(handle_one_xevent): Save visible state go generate ICONIFY_EVENT
properly.
* nsterm.m: Ditto.
(windowDidDeminiaturize): Generate DEICONIFY_EVENT.