title: FileField: force using TemporaryUploadedFile
body: <p>When uploading a file for a field such as this one:</p>
  
  <pre><code>file = FileField(upload_to='/path/')
  </code></pre>
  
  <p>Django uses either an <code>InMemoryUploadedFile</code> or a <code>TemporaryUploadedFile</code>. The latter is stored on the disk and its file name can be accessed with the <code>temporary_file_path</code> property. The storage choice depends on the file size.</p>
  
  <p><strong>How can I override this behaviour and always upload as a <code>TemporaryUploadedFile</code> for this model field?</strong></p>
  
  <p>The reason I am asking this is because I need to write a validator that uses an external library that can only take file paths as input, no data streams.</p>