This commit introduces a few ready made effects for the 3D viewport
and OpenGL rendering.
Included effects are Depth of Field, accessible from camera view
and screen space ambient occlusion. Those effects can be turned on and
tweaked from the shading panel in the 3D viewport.
Off screen rendering will use the settings of the current camera.
WIP documentation can be found here:
http://wiki.blender.org/index.php/User:Psy-Fi/Framebuffer_Post-processing
