Photon Tracer Subsurface Scattering

[hhergeth]

The Photon Tracer integrator computes incorrect results for subsurface scattering(much too bright)

[hhergeth]

This is actually more difficult.
Redesign the ParticleProcess to include correct behavior for checking if the particle is undergoing a refraction event. If so do subsurface scattering if necessary.
This will then result in the same behavior in Progressive Photon Mapping and Photon Tracing.