avoid non-negativity in cosine-terms... is this correct?
Hm... Changes some minor things/mistakes... But I'm actually completely confused.
Ignore eye-cosine factor in geometry term if sample is specular - no idea if this makes sense.
Fixed Sphere. xD Thanks @panmari for your incredible smartness. ^^
Handle point lights, adapted XYZGrid, handle specular shadingSamples in PathTracer
Separate MAX_BOUNCES for light and eye subpaths
Tried to somehow include specularity in BDPathTracer - better result.

However: Many Light and few eye bounces should lead to visible caustics which is not the case!