Archlinux support

This adds support for Arch Linux/Arch Linux ARM. It has been around in my repo for a long time now, with a good number of users I believe, and rarely has issues.

First 3 commits are not directly related to arch, but necessary (especially the last 2).
dmz-cursor-theme is needed on Debian to have pretty non-X-default cursors.
libgl1-mesa-dri is needed to have software GLX.