(gamegrid-face): new variable to emulate a buffer-local default face.

(gamegrid-face): new variable to emulate a buffer-local default face.
(gamegrid-xbm): new variable; XBM image as a replacement for
`gamegrid-xpm' on Emacsen compiled without XPM-support.
(gamegrid-colorize-glyph): Ported XEmacs-code for the generation
of images to Emacs.
(gamegrid-match-spec): Call `gamegrid-make-image-from-vector' to
convert XEmacs-type image descriptors.
(gamegrid-color-display-p): Removed. (Use `display-colors-p' instead.)
(gamegrid-make-image-from-vector): New function. Convert XEmacs'
image descriptors.
(gamegrid-display-type): Use Emacs' standard `display-.*-p'
functions to check for display capabilities. Fix the recognition
of image-support in Emacs 21 by this way.
(gamegrid-hide-cursor): Removed.
(gamegrid-setup-default-font): Ported the code from XEmacs to
Emacs: create a new face and assign the variable `gamegrid-face'
to it. Make sure that the face is not higher than the smallest
image used by the game.
(gamegrid-initialize-display): Use `(setq cursor-type nil)'
instead of `gamegrid-hide-cursor'.
(gamegrid-set-face): If `gamegrid-display-mode' is 'glyph, put an
image in the buffer, instead of applying a face.
(gamegrid-init-buffer): If `gamegrid-display-mode' is 'glyph, put
the face held by `gamegrid-face' in an overlay over the whole
buffer to emulate a buffer-local default-face.