title: django forms - rendering vertical checkboxes for M2M
body: <p>I would like use vertical checkboxes for M2M. Here's a code sample:</p>
  
  <pre><code>class Contact(models.Model):
      ...
      groups = models.ManyToManyField (
          Group,
          related_name = "contacts",
          verbose_name = _("Groups"),
      )
      ...
  
  class Group (models.Model):
      name = models.CharField (
          unique = True,
          max_length = 100,
          db_index = True,
      )
  
  class ContactAdminForm(forms.ModelForm):
      class Meta:
          model = Contact
  
      radio_fields = {"groups": admin.VERTICAL} # only for foreignkey or for choices
  </code></pre>
  
  <p>Any help for it?</p>
  
  <p>thanks,
  V.</p>