bug#58002: 29.1: Sokoban: obsoletion warnings in gamegrid

[Mattias Engdegård]

On Emacs master, starting Sokoban (from GNU ELPA) results in several warnings:

> Warning (gamegrid): Using obsolete XEmacs style "glyph"; convert to an Emacs 
> image-spec instead

which apparently is from

> (defvar sokoban-target-options
>   `(((glyph
>       [xpm :data ,sokoban-target-xpm])
[...]

where (after some digging) it seems that the vector needs to be

      ((:type xpm :data ,sokoban-target-xpm :ascent center)))

somewhat non-intuitively, because of the slightly alarming line

>          (find-image data)) ;untested!

in gamegrid.el. Suggested patch attached.
Is this all correct and as desired? Does it break anything when using old Emacs 
versions?

sokoban-warning.diff
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