Blender Git Loki

Cycles: Camera frustum space object culling scene simplification

The idea is to give artists a simplier way to control memory usage in such
scenes as grass fields by doing automatic object culling based on whether
object is visible in the frame or not.

This is controlled on per-object level. In order to use this option few steps
are required:

- Enable Simplify in scene settings

- Enable Camera Cull option in the Simplify panel

- Set camera cull margin (measured in relative value to the render resolution)
This setting is used to avoid possible flickering caused by changes in shadow
which are cast by objects outside of the frame.

- Enable Camera Cull for objects which are desired to be culled
(object culling option could be found in Option panel in object buttons).

There is still room for improvements, but this worked quite well during
Gooseberry open movie project, so think it's useful feature even in it's current
non-ideal state.