bug#12218: 24.2.50; vc-ediff: Pressing `n' moves focus away from ediff control panel

[Juri Linkov]

>> I can't reproduce it on Gnome 2 (Metacity), but the screenshot shows
>> that OP uses Xfce (Xfwm).
>
> Issues happens for me with XFCE and M-x ediff all the way back to at
> least Emacs 22.3.

As I see Ediff selects the frame using `raise-frame' and
`set-mouse-position' instead of `frame-focus' as would be
more natural to do.  Maybe this is the cause of this problem.