add libcap_ng
SELinux fixes and updates to 2012-09-24
Merge branch 'p/selinux' of git://github.com/vcunat/nixpkgs

This branch adds libcap-ng and updates SELinux. It doesn't seem like
anyone is actually using SELinux from nixpkgs, but everything compiles
and looks right.

Signed-off-by: Shea Levy <shea@shealevy.com>