Update session file for Cinnamon 2.0

Cinnamon now has it's own cinnamon-session and no longer uses gnome-session.
Fix two bugs:

* Set proper perms on /dev/* entries inside PBI container
* Add some locking when doing nullfs mounts, since doing two at once seems to deadlock the system
When upgrading system, remove / re-create PBI icons
Turn on some build options for libxine
Merge branch 'master' of github.com:pcbsd/pcbsd