detecting supported opengl extensions

[NaN]

I've fixed the checks. The graphics implementation is Joe's baby. I hope he can comment on the other stuff.

With this change vdrift says INFO: Your video card doesn't support floating point textures. Disabling shaders.
instead of crashing on FBO initialization, if one uses Mesa.

Mesa supports frame buffer objects(this is where most cards will bail out I think) but not floating point textures?

Edit: Feel free to post a patch if you hit bugs.