adding support for hibernation to xfce4-sessions's exit dialog

[Jani Monoses]

> Well, the "API" depends on the service interface, which is different for
> various applications (just compare Thunar and Terminal). You could add
> something like KUniqueApplication, but that doesn't make things easier
> in most cases, IMHO.

The Gnome SoC project working on this.
http://live.gnome.org/SingleInstanceApps