[Bf-cycles] Adding compositors to the interactive preview

[Nikhilesh Sigatapu]

Would it be a good idea to have the interactive render preview go 
through compositing too (as an option)? It doesn't seem to hard to do - 
just call 'ntreeCompositExecTree()' after proper setup? The interactive 
preview could show up as an input in the nodes, and have an output back 
into the preview. May also help set up noise filtering for the preview.

The problem is though that Blender's compositing is CPU only (I think) 
and so it might not work well with GPU preview.

-- 
Nikhilesh S
http://www.nikhilesh.info