[Bf-cycles] Render Layers - Camera Override

[Zauber Paracelsus]

I'd like to propose a small enhancement for Render Layers: the ability 
to override the scene's camera.

One use case that comes to mind would be to split a scene's rendering 
into multiple 'layers' based on distance, with each scene using a camera 
with different start/end values for clipping.  Camera one may be 1cm to 
10m, while camera two is 10m to 1000m.  This can already be done 
manually by rendering twice with two different clipping values for each 
render and then compositing them together manually.  However, this would 
simplify the approach, making it easier to do such renders for animations.

One could also just set the clipping values to 1cm to 1000m, but when I 
tried this in the past it caused artifacts and errors to appear in the 
render, due to floating point precision errors.