mendel printable frame updated

I've been looking at this thing for a while and decided I wanted to play with it, but I run on linux, and don't use wine, so I cannot run Google sketchup. Also, I'm just learning how to use OpenSCAD, so I remade it with OpenSCAD. Finally, the design was too big to print on my ToM.

*UPDATE* The corner-piece is now "2-manifold".