Blender Git Loki

Image Editor: Make Rendering of Pure Emissive Colors Optional

There are some areas that don't handle pure emissive colors well. For
example erasing alpha using 2d or 3d painting. Or blurring an image in
the compositor.

This patch makes the rendering of pure emissive colors optional. In the
side panel of the Image editor it can still be enabled when needed.

There currently isn't a better place to store it as it is related on how
the image (or a layer of the image) is created. A future design needs to
make sure that the full workflow is supported.