glib: minor update and patch malloc usage

It's mainly a work-around to make skype work again.
It also seems to stabilize xfce4-session crashes (on my setup)
https://bugzilla.xfce.org/show_bug.cgi?id=9709
xfce4session: make it systemd-aware

This should solve many issuses, including:
 - show mountable volumes and mount-on-click (in Thunar)
 - fix shutdown actions (and don't ask for password anymore)

It doesn't explicitly depend on anything in x-updates,
but AFAIK noone has tested it against master (yet).
Connected to #441.