title: Django "Save as new" and keep Image fields
body: <p>I have a Django model with multiple ImageFields.</p>
  
  <p>On the ModelAdmin class I've set <code>save_as = True</code>, which means The admin page has a "Save as new" button, which allows for duplicating an existing item and saving it as new.</p>
  
  <p>However when this button is used, the ImageFields are not duplicated and are left blank on the new item. </p>
  
  <p>Looking at the POST request, I see that these fields are blank in the post data. </p>
  
  <p>I've thought about overriding the Model class' save method, and copying the images from the old object by myself. But as far as I could figure out, I have no way to tell that the object is saved "as new". I also don't seem to have the ID of the old Item so I cannot get the old Images from it.</p>
  
  <p>Is there a way to get these image fields to be duplicated as well?</p>
  
  <p><strong>Edit:</strong>
  Added Example code by request.</p>
  
  <p>Created a minimalistic app with only one model. Verified problem still occurs.</p>
  
  <p>Sample models.py:</p>
  
  <pre><code>from django.db import models
  
  class Person(models.Model):
      face_image = models.ImageField(upload_to='images', 
                                     null=False, 
                                     blank=True)
  </code></pre>
  
  <p>Sample admin.py:</p>
  
  <pre><code>from django.contrib import admin
  from testapp.models import Person
  
  class PersonAdmin(admin.ModelAdmin):
      save_as = True
  
  admin.site.register(Person, PersonAdmin)
  </code></pre>