Blender Git Loki

Image Py API: Expose 'load_exists' to RNA image load(), and extend load_image() helper.

Expose our `BKE_image_load_exists` feature through an optional parameter to `Image.load()`.

Extend `image_utils.load_image()` with two optional parameters, to return existing image datablock
if possible, and in that case, to force reloading said image.

Needed by incomming 'import images as planes' addon enhancement.