Added Disney BRDF to OSL BSDF list.
Merge pull request #553 from est77/master

Added Disney BRDF to OSL BSDF list.
No need to exec the OSL shader in physical surface shader.
Added sppm test scene, removed old transparency test scene.
Merge pull request #554 from est77/master

OSL fixes and improvements.
Merge remote-tracking branch 'upstream/master' into est_OSL
Fixed PR comments.