Blender Git Loki

* Slight change to lamp energy calculation - make lamps invisible
for shading if their 'visibility factor' is below 0.001. This
gives no perceptible visual difference in my tests, but can
significantly speed up shading when using lots of omni lights
with quad falloff over a large area. Since quad lamps never
actually fall off to 0, previously every lamp would be considered
for shading each pixel, even if such lamps had a tiny falloff
distance, and were miles away.