Refracting bunny

Hopefully bug free this time. I fixed the error where paths including a diffuse or glossy material and ending with Transmit->Light (or "direct caustics" I guess) where not contributing energy, and things are looking a lot better.

Next up is performance improvements, and running some contrived tests to ensure things are still unbiased and otherwise visually behaving like expected.

1024x1024, two area lights, glass material with an ior of 1.55, a whole lot of pixel samples.

 

-Espen