title: Django ImageField core=False in newforms admin
body: <p>In the transition to newforms admin I'm having difficulty figuring out how specify core=False for ImageFields.</p>
  
  <p>I get the following error:</p>
  
  <pre><code>TypeError: __init__() got an unexpected keyword argument 'core'
  </code></pre>
  
  <p>[Edit] However, by just removing the core argument I get a "This field is required." error in the admin interface on attempted submission. How does one accomplish what core=False is meant to do using newforms admin?</p>