In the GTK3 port we mistakenly moved from using the EggSMClientXSMP
class to the (stub-like) EggSMClient base class for Sugar's XSMPClient
class, instantiated for every activity.
This meant that the GTK3 activities weren't registering with the
session manager, meaning that they won't automatically save their work
when the user shuts down, and they can't inhibit shutdown, etc.
Restore this functionality by adding the appropriate header so that
EggSMClientXSMP is introspectable, and then use it from the Python code.
Acked-by: Simon Schampijer <simon@laptop.org>
Daniel Drake