Using XDG for retrieving downloads dir on Linux/Mac.
Merge branch 'blueprints-downloads' of https://github.com/Prototik/BuildCraft into Prototik-blueprints-downloads
Default download location is computed only once, as to make it more explicit
to the user where things are located and how to fix.
Merge branch 'Prototik-blueprints-downloads' into 6.0.x