Cycles: Render Passes

Currently supported passes:
* Combined, Z, Normal, Object Index, Material Index, Emission, Environment,
  Diffuse/Glossy/Transmission x Direct/Indirect/Color

Not supported yet:
* UV, Vector, Mist

Only enabled for CPU devices at the moment, will do GPU tweaks tommorrow,
also for environment importance sampling.

Documentation:
http://wiki.blender.org/index.php/Doc:2.6/Manual/Render/Cycles/Passes

intern/cycles/render/object.h

@@ -41,6 +41,7 @@ public:
 	Transform tfm;
 	BoundBox bounds;
 	ustring name;
+	int pass_id;
 	vector<ParamValue> attributes;
 	uint visibility;