bug#7847: insert-sliced-image bug on darwin

[Alan Third]

Antonio Santos <antonio@santosvelasco.com> writes:

> It appears I've experienced this (or a very similar issue) recently.
>
> The order of the sliced images is reversed when evaluating
>
> (progn
>   (let ((image (find-image '((:type xpm :file "delete.xpm")))))
>      (insert "\ntop: ")
>      (insert (propertize " " 'display `(,image (slice .0 .0 1.0 0.5))))
>      (insert "\nbuttom: ")
>      (insert (propertize " " 'display `(,image (slice .0 .5 1.0 1.0))))))
>
> I'm using OS X as well.

Images in NextStep have an inverted Y co-ordinate and it looks like it
was forgotten about when handling slices.

I've pushed a fix to master.
-- 
Alan Third