This is a simple cleanup commit, I'm submitting as a patch because the regression test fails on light_spread.blend and area_light_uv.blend. This is due to numerical issues, if I change normalize_spread from 1.0f / (1.0f - half_spread * cot_half_spread) to 2.0f / (2.0f + (2.0f * 0.5f * (M_PI_F - 2.0f * half_spread) - M_PI_F) * cot_half_spread) (as the way computed before), the regression test would pass. I guess we could just update the images in the regression test, but I don't know how.
This is a comparison of the values of normalize_spread before and after the patch: