bug#2845: 23.0.92; 'Save Options' does not save font setting

[Adrian Robert]

> (defun ns-respond-to-change-font ()
>   "Respond to changeFont: event, expecting ns-input-font and\n\
> ns-input-fontsize of new font."
>   (interactive)
>   (let ((face 'default))
>     (set-face-attribute face t
>                         :family ns-input-font
>                         :height (* 10 ns-input-fontsize))
>     (set-face-attribute face (selected-frame)
>                         :family ns-input-font
>                         :height (* 10 ns-input-fontsize))
>     (let ((spec
>            (list (list t (face-attr-construct 'default)))))
>       (put face 'customized-face spec)
>       (custom-push-theme 'theme-face face 'user 'set spec)
>       (put face 'face-modified nil))))

This would change the behavior of the font panel in other  
circumstances so that it wouldn't just set the font of the current  
frame.  Also it seems to work around the functionality in menu-set-font.

We might need to implement x-select-font to put up a font panel and  
return the result (without doing any actual setting of anything itself).