Session client support in libxfce4ui

[Nick Schermer]

I'd like to know that kinda client session support we want in
linxfce4ui, which means, how complicated do we want it to be? Only a
bunch of simple signals that allow applications to save, die etc? In a
way it's suitable for Xfce (and hopefully also Thunar) or a bit bigger
like GnomeClient?

I know this is a difficult topic since Gtk+ and the Gnome folks are
struggling with it for years, but we now have to opportunity to create
something good.

Nick