bug#69983: Use category for display-buffer-alist

[martin rudalics]

> In any case, if you are suggesting to change the "random" place where
> warnings are displayed, we should first discuss that, because your
> assertion that no one will dislike the change sounds very much like
> famous last words to me, so to speak ;-)

This part

+                                   '(display-buffer--maybe-at-bottom
+                                     (window-height . (lambda (window)
+                                       (fit-window-to-buffer window 10)))

would hard-code a new preference which might cause problems indeed.  But
the subsequent

+                                     (category . warning)))))

would allow users to customize the display of warnings via
'display-buffer-alist' and cannot harm otherwise.

martin