Approximate AO: Diffuse Bounce Hack

This brings back the single bounce indirect diffuse lighting for AAO,
it's not integrated well but that will be tackled later as part of
shading system refactor and subdivision changes. The caveats are the
same as AAO, with one extra thing, the diffuse lighting is sampled once
per face, so it will not be accurate unless faces are subdivided.

I'm committing this now so we can start testing it for Durian, and
since changes need to make it work properly are planned.

release/scripts/ui/properties_world.py

@@ -219,6 +219,7 @@ class WORLD_PT_ambient_occlusion(WorldButtonsPanel):
 
         col = split.column()
         col.prop(ao, "energy")
+        col.prop(ao, "indirect_energy")
 
         if wide_ui:
             col = split.column()