Added initial support for Debian/kFreeBSD

This patch enables Lumina to build/run on Debian's kFreeBSD port, a branch of Debian which marries the FreeBSD kernel (and ZFS) with the GNU userland utilities and Debian's APT package manager.
The attached patch builds and runs for me on PC-BSD 10.0, Ubuntu 14.04 and Debian/kFreeBSD 7.
On the Debian/kFreeBSD platform Lumina runs and can launch programs, and manage application windows. However, audio volume, screen brightness and battery monitoring are not yet supported.