title: django error using autocomplete_light
body: <p>I'm trying to use autocomplete-light in a form field.
  When I'm trying to use the field I get 
  <code>FieldError at /autocomplete/icd_10Autocomplete/
  Cannot resolve keyword u'name' into field. Choices are: icd_10_code, icd_10_desc, id</code></p>
  
  <p><code>icd_10_code, icd_10_desc, id</code> are the fields from icd_10 table but I want to retrieve data only form <code>icd_10_codes</code> field.</p>
  
  <p>icd_10_code in Diagnosis model is a foreing key in icd_10.icd_10.code field. When I'm trying to write a value in Diagnosis.icd_10_code I want the form to autocomplete the word, looking words stored in icd_10.icd_10_code fields.</p>
  
  <p>Any idea?</p>
  
  <p><strong>forms.py</strong></p>
  
  <pre><code>import autocomplete_light
  
  autocomplete_light.register(icd_10)
  autocomplete_light.autodiscover()
  
  class DiagnosisForm(forms.ModelForm):
      def __init__(self, *args, **kwargs):
          super(DiagnosisForm, self).__init__(*args, **kwargs)
          self.helper=FormHelper(self)
          self.fields['icd_10_code']= forms.ModelChoiceField(queryset=icd_10, widget=autocomplete_light.ChoiceWidget("icd_10Autocomplete"))
  
          self.helper.layout = Layout(
              # 'patient',
              'age_of_diagnosis',
              'icd_10_code',
  
              FormActions(
                  Submit('submit', "Save changes"),
                  Submit('cancel',"Cancel")
              ),
          )
          self.helper.form_tag = False
          self.helper.form_show_labels = True
  
      class Meta:
          model = Diagnosis
  </code></pre>