Replace existing image

Forgive me if this has been requested elsewhere, but I've not seen it in the queue through the last year...

I'd like to have the option (as an administrator) when a file already exists to:

- Keep the existing file, renaming the old one (slightly different than the current behavior), or
- Replace the existing file

Currently, ImageField renames the new file, resulting in image_0.jpg, image_1.jpg, etc. This has the potential to bloat the images directory, which this user doesn't need.