Blender Git Loki

Better implementation of threading for split lnor code.

Not that much satisfied yet, though, this adds some complexity with not-so-much gain in the end
(about 33% better with 100000 loops and more, on an 8cores machine - with nearly no gain after 4
workers anyway)...

Have the feeling threadable parts of this func are too small chunks needing too much data
to be really efficient (since we can't parallelize the main loop, order is crucial here).