unix filenames

Hi Tobi, 

this is a great cheat cheat and I will give it to my students! Reading it I noticed 2 little things that I'd like to improve, hence the pull request.
About the license, for content type stuff like this I usually use a Creative Commons License like this one:
http://creativecommons.org/licenses/by-nc-sa/3.0/de/

Cheers

Béla