Blender Git Loki

Change previous commit that uses transparency by default.

Sampling still samples the texture color in transparent areas. This is
not so bad but users may get confused when clicking on a white spot and
picking black instead of the mesh color.

Krita also has this uncertainty when picking in transparent areas but we
do not interpolate with an explicit "transparent" looking texture during
viewport drawing (maybe we should), so it's not so apparent what happens
here.