title: Django Admin: change select box for foreign key to search autocomplete, like search objects
body: <p>The Django admin panel has a search autocomplete with <code>search_fields</code> on the list of objects of a model, but right now I have 3000 users. To add a user manually is dificult with the selectbox; I need the same behavior like the searchfields for selecting a user foreinkey <code>User</code>.</p>
  
  <p>How can I include the Django search feature on the form for editing inside the admin panel?</p>
  
  <pre><code>from myapp.models import Red 
  from django.contrib.auth.models import User
  
  class Red(models.Model):
      customer = models.ForeignKey(User, verbose_name="Cliente")
      pub_date = models.DateTimeField(default=datetime.now, blank=True)
  </code></pre>