[Fluxus] obj files

[Dave Griffiths]

Hi all,

I've rewritten the obj load and save in C++, as it was taking far too
long in scheme, and started unifying load and save for all primitives,
so, new commands:

(load-primitive filename) loads a prim from disk
(save-primitive filename) saves current prim to disk
(clear-geometry-cache) loading is cached, so this clears it

currently loading .obj files result in polyprims, png files result in
pixel primitives.

cheers,

dave