Blender Git Loki

Image: refactor image_load_image_file() function as suggested on review

I still need to do the same treatment for image_load_movie_file()
(and potentially for image_load_sequence_file() I have to check if it's
also the case)

Some of the image loading routines in the sequencer could have this
treatment as well.

Also I think that the whole:

"image is an ID block which might be used by multiple users. it should be
self-contained in terms what it is."

Is not a problem anymore. But I need to dig further, because I don't
remmeber if we are using ImageView elsewhere or not.