Blender Git Loki

Assuming the freeze is over and we can head towards 2.34: this is the
first commit for review and improvements on OSA (anti aliasing) in
Blender.

http://www.blender3d.org/cms/Rendering_engine.320.0.html

Most relevant changes:
- full check on subpixel sample locations
- all subpixels are fully rendered (gives spec AA, procedural texture AA)
- also unified render uses it
- removed double-used code for unified render

Whether or not this will be optional (better pics, but in some cases slow)
is to further evaluate. For raytracing - for example - this cannot be simply
done, since the new sampling system made raytrace code much simpler.