Inspired by http://www.tedunangst.com/flak/post/xautobacklight .
Pretty much the same code but with privileged ioctl functions removed in favour
of fork/exec of xbacklight. I'm not yet using the gamma correction function
since it causes some weird display issues on my machine.
Compile with:
cc -std=c99 -O2 -I /usr/X11R6/include -L /usr/X11R6/lib -lX11 -lXrandr -o xautobacklight xautobacklight.c