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/kernel/kernel_object.h

@@ -64,5 +64,15 @@ __device_inline float object_surface_area(KernelGlobals *kg, int object)
 	return f.x;
 }
 
+__device_inline float object_pass_id(KernelGlobals *kg, int object)
+{
+	if(object == ~0)
+		return 0.0f;
+
+	int offset = object*OBJECT_SIZE + OBJECT_PROPERTIES;
+	float4 f = kernel_tex_fetch(__objects, offset);
+	return f.y;
+}
+
 CCL_NAMESPACE_END