PolicyKit authentication agent changes

[Matthias Clasen]

As of version 0.100 (which will land in F15 as a post-alpha update), the
polkit-gnome package will no longer install an autostart file for
polkit-gnome-authentication-agent-1. Instead, each desktop environment
is reponsible for making sure that an authentication agent is running.

For GNOME, this is done by gnome-session installing an autostart file
with OnlyShowIn=GNOME;. Other desktop environments that rely on
polkit-gnome need to do something similar.