title: Django form not saving with ModelChoiceField - ForeignKey
body: <p>I have multiple forms on my site that work and save info to my PostgreSQL database. 
  I am trying to create a form to save information for my Set Model:</p>
  
  <pre><code>class Set(models.Model):
      settitle = models.CharField("Title", max_length=50)
      setdescrip = models.CharField("Description", max_length=50)
      action = models.ForeignKey(Action)
      actorder = models.IntegerField("Order number")
  </code></pre>
  
  <p>The Set Form looks like this. I am using ModelChoiceField to pull a list of Action name fields from the Action model, this displays on the form as a select dropdown</p>
  
  <pre><code>class SetForm(ModelForm):
  
      class Meta:
          model = Set
          fields = ['settitle', 'setdescrip', 'action', 'actorder']
      action = forms.ModelChoiceField(queryset = Action.objects.values_list('name', flat=True), to_field_name="id")
  </code></pre>
  
  <p>The view for createset is below: </p>
  
  <pre><code>def createset(request):
      if not request.user.is_authenticated():
          return redirect('%s?next=%s' % (settings.LOGIN_URL, request.path))
      elif request.method == "GET":
          #create the object - Setform 
          form = SetForm;
          #pass into it 
          return render(request,'app/createForm.html', { 'form':form })
      elif "cancel" in request.POST:
          return HttpResponseRedirect('/actions')
      elif request.method == "POST":
      # take all of the user data entered to create a new set instance in the table
          form = SetForm(request.POST, request.FILES)
          if  form.is_valid():
              form.save()
              return HttpResponseRedirect('/actions')
          else:
              form = SetForm()
              return render(request,'app/createForm.html', {'form':form})
  </code></pre>
  
  <p>When the form is filled in and valid and Save is pressed, nothing happens. No errors, the page just refreshes to a new form. 
  If I don't set the action field in forms.py using (action = forms.ModelChoiceField(queryset = Action.objects.values_list('name', flat=True), to_field_name="id")) then the data saves, so that is likely where I am doing something wrong. Just not sure what?</p>