Bug#744264: mate-session-manager: systems logs out when invoking shutdown ore reboot

[Stefano Karapetsas]

This is the fix for the build on non-linux kernel: 
http://anonscm.debian.org/gitweb/?p=pkg-mate/mate-session-manager.git;a=commitdiff;h=95cea3dc138cde48ed11542be518978b0d542884
When compiled with systemd support, mate-session detects systemd at 
runtime. Maybe something is wrong with this detection on Jessie, but 
mate-session with systemd works well on all other distributions.