Blender Git Loki

SSAO shader.

This works by using the calculated view space normal and accumulating
coverage of a certain area by nearby pixels. There are two sliders to
control the effect:

* Scale controls the area around each pixel that the shader "collides"
against
* Darkening scales the occlusion effect.

The effect works, but due to the way the normals are calculated, the
normals are never smooth shaded (that would require a separate render
target to store them) and the edges or polygons can be too apparent.
This is not really fixable at the moment unless we move to deferred
pipeline.

The FX system is stll not well optimized and rendering does not always
work correctly, but it's good to have this out for people to play with.