[fluxus] multitexturing and frustum stuff

[dave]

* (clip front back) sets the clipping plane positions, defaults to 1
10000

* (frustum top bottom left right) sets screen area, with this you can
set the aspect ratio for the render. defaults to -0.75 0.75 -1 1

* (hint-multitex) turns on multitexturing

* (multitexture n texture) loads a texture into multitexture slot n.
apart from slot 0 (which is the original texture "t") textures look for
pdata texture coordinates called "tn" where n is the multitexture slot
number. you have to create these yourself.

* orthographic fixes - mouse zoom works, editor projection fixed

* crashfix for pdata-copy

* documentation update - still a bit behind the code tho...

cheers,

dave