title: Maintain old filename while updating with carrierwave
body: <p>With carrierwave, I'd like to change the image without changing the location(filename). This way, all links to the old image will still work, but point to the new picture.</p>
  
  <p>For example, I upload an image 'promotion1.png'. I link to this image in an editor. Afterwards, I have a new promotion (promotion2.png), and want to update the image without having to go to the editor again. So old filename points to the new file.</p>
  
  <p>How can this be done? I don't want to be forced to use the same filename. I = an unwitting client :)</p>