Blender Git Loki

Cycles: Remove confusing labels usage in hair BSDF

BSDF sampler function shouldn't give labels it's not intended to do.
That said reflection shouldn't give transmission ray and transmission
give reflection ray.

Added an assert in the transmission sampling but reflection still
needs some investigation because even after recent fixes the check
for projection onto the reflected ray could give both positive and
negative values.

It shouldn't have any affect on renders just makes internal logic
consistent and unleashes an issue to be investigate further.