title: django admin, set choice field length?
body: <p>im trying to set the ChoiceField length in my django form, I used the below:</p>
  
  <pre><code>from django.forms import TextInput, Textarea, ChoiceField
  
  class SiteAdmin(admin.ModelAdmin):
      formfield_overrides = {
          models.CharField: {'widget': TextInput(attrs={'size':'25'})},
          models.ChoiceField: {'widget': TextInput(attrs={'size':'25'})},
          models.GenericIPAddressField: {'widget': TextInput(attrs={'size':'25'})},
      }
      ...
  </code></pre>
  
  <p>and then got the error:</p>
  
  <pre><code>  File "/var/www/infternal/sites/admin.py", line 18, in SiteAdmin
      models.ChoiceField: {'widget': TextInput(attrs={'size':'25'})},
  AttributeError: 'module' object has no attribute 'ChoiceField'
  </code></pre>
  
  <p>Does anyone know what i need to alter to change the select/dropdown length?</p>
  
  <p>Thanks</p>