Misc. improvements / fixes

- Fixed gcc compile error.
- Compatibility with latest OIIO / OSL releases (SIMD optimizations).
- Added OSL texture test scene.
- Fixed OSL test scenes sphere uv coordinates.
- Started de-duplicating things in test scenes.
- Formatting changes.

I'm just curious about all this #if stuff. Do you think we should not just support stable osl and oiio versions? I just ask.