X11 tests for all de/wm

This adds tests for all de/wm combinations, that can be run using the `w` prefix.

Sample runs: `2014-11-14_22-17-28_drinkcat_chroagh_x11test_w` and `2014-11-14_22-17-38_drinkcat_chroagh_x11test_x`.
Yeah, at first I was using `import`, but it does not handle obscured windows well:
http://www.win.tue.nl/~aeb/linux/misc/import/screenshot.html
e.g. for DEs that display a dialog on startup, you end up with a black square in the middle of the screenshot...