Re: Renaming non-X x_* procedures in xdisp.c (and elsewhere)

[Alex]

I'm back to working on this now. I have a few disjointed questions, but
for now I'd like to ask:

* What's your opinion on changing FRAME_WINDOW_P to basically a C
  version of display-graphics-p? This would move toward using multiple
  windowing systems simultaneously, and helps clear the intent of the
  predicate. I searched and only found uses of it being used as a
  boolean.

* To get rid of a few FRAME_X_WINDOW calls in frame.c and all of the
  FRAME_X_OUTPUT (f)->* calls in xdisp.c I'm considering adding a new
  function pointer interface frame_output_interface, which would allow
  for a generic interface to common output_data elements. Would you be
  open to this? For example, the following:

    FRAME_X_OUTPUT (f)->nontext_cursor

  would be changed to something like:

    FRAME_OI (f)->get_nontext_cursor (f);

  And the FRAME_X_WINDOW calls in frame.c to:

    FRAME_OI (f)->have_native_window (f);

* Why is the font structure within a frame's output_data instead of in
  the frame itself? I was considering adding it to the above interface,
  but I see no immediate reason why it's considered device-dependent.