title: change sort order of modelchoicefield django
body: <p>how can I change the order of the values in the ModelChoiceField billing_company?</p>
  
  <p>models.py</p>
  
  <pre><code>class Company(models.Model):
      name = models.CharField(max_length=30, unique=True)
  </code></pre>
  
  <p>forms.py</p>
  
  <pre><code>billing_company = forms.ModelChoiceField(Company.objects, required=True)
  </code></pre>
  
  <p>Thanks for your help.
  Tom</p>