* Projection painting files reside in paint_image_proj.c
* 2d projection files reside in paint_image_2d.c
* Common operator/paint operation code resides in paint_image.c
All old code layout is out. Phew...Now we can at least concentrate on
each system separately when debugging this beast. We could even separate
the paint structs for 2d/projective more easily should we choose to do
so.