Upgrade to remove triangle reference duplication

[pshriwise]

Right now there are two triangle references per triangle: one with a forward sense in its scene (volume) and another for the reverse sense in its scene (another volume).

We may be able to avoid the need to duplicate these references by storing the forward and reverse sense scenes on the GeometryData object -- it should be available to us as part of the intersection arguments. The remaining need is to know what scene the ray is being fired on. This information can be stored on the RTCDRay if needed, but it may also be available as part of the intersection arguments. TBD.

[pshriwise]

Doesn't look like the scene information is part of the RTCIntersectionArgs struct:

struct RTCIntersectFunctionNArguments
{
int* valid;
void* geometryUserPtr;
unsigned int primID;
struct RTCRayQueryContext* context;
struct RTCRayHitN* rayhit;
unsigned int N;
unsigned int geomID;
};

so it will need to go on the ray.