[dwm] xgamma notify

[pancake]

I have been playing a bit with xgamma and I think it can be useful as a 
graphical
notification for important alerts like low battery or so.
The usage is quite simple. and we can 'flash' the screen in red for a 
fraction of a second with:

$ cat flash.sh
for a in $(seq 1 $1); do
 xgamma -ggamma 0.3 -bgamma 0.3
 sleep 0.1
 xgamma -gamma 1
 sleep 2
done

$ sh flash.sh 10

--pancake