Make sure the shader execution heap is cache aligned

[lgritz]

No description provided.

[lgritz]

@AlexMWells

[AlexMWells]

 if (shadingsys().debug())
        infof("  ShadingContext %p growing heap to %d",
              static_cast<void*>(this), heap_size_needed);

Do you care/mind if you no longer receive this debug info about heap growing? Could add it back to the new helper function. I have no need, just noticed it won't be there anymore.

[lgritz]

No, I thought about that when I deleted it. I don't think it's served any real purpose, so I was ok letting it go.

[AlexMWells]

LGTM

[fpsunflower]

LGTM2! I like this way better!