fixes #245: use alternate datafiles location

Hi,

This is proposed fix for #244, #245.

Looks like `$XDG_DATA_HOME` (or default to `~/.local/share`) works as an alternate data files location when installing within a virtualenv. I can confirm that both virtualenv and global installations work (along with dekstop entry, locales etc) with this changeset, atleast on ubuntu 13.04.

Cheers.