Cycles: enable improved closure sampling, this should give less noise for mix, add

and glass shaders. How well this will work on non-fermi GPU's is unclear still, it's
a bit heavy on register usage.

intern/cycles/render/scene.h

@@ -109,7 +109,7 @@ public:
 	SceneParams()
 	{
 		shadingsystem = SVM;
-		use_multi_closure = false;
+		use_multi_closure = true;
 		bvh_type = BVH_DYNAMIC;
 		use_bvh_cache = false;
 		use_bvh_spatial_split = false;