ray: stop recurring below a relevance threshold

There's no point computing more reflections if they're not going
to contribute substantially to the resulting sample.  Previously
the max depth threshold solely controlled how many times a given
ray could reflect, this commit introduces a minimum relevance as
well.  Value may require tuning, may actually make sense to move
into the scene description as a parameter.

Brings a minor frame rate improvement.

0 files changed, 0 insertions, 0 deletions