title: Replacing a Django image doesn't delete original
body: <p>In Django, if you have a ImageFile in a model, deleting will remove the associated file from disk as well as removing the record from the database.</p>
  
  <p>Shouldn't replacing an image also remove the unneeded file from disk?  Instead, I see that it keeps the original and adds the replacement.</p>
  
  <p>Now deleting the object won't delete the original file only the replacement.</p>
  
  <p>Are there any good strategies to doing this?  I don't want to have a bunch of orphan files if my users replace their images frequently.</p>