Blender Git Loki

3D Textures:

If we fail allocating a proxy texture don't fail, instead create a
smaller nearest filtered image to display in its place.

This can make viewing slow (it's an extra O^3 operation), but this will
probably help us render the tornado in 3D viewport in gooseberry and
still actually see something - despite the rendering taking longer.
I've added a debug print so we can know when this happens.