title: Django MultipleChoiceField choices of users throws error
body: <p>I am trying to write a form that allows the user to select as many users from a specific group as they want. However when I try to use the list of users as an option I get an error saying that 'User' object does not support indexing.</p>
  
  <p>Its a fairly standard form, the main difference is that the group is filtered based on a kwarg passed to the form. The form is passed a project_id (project object primary key) and it then finds the group associated with that project and generates the field.</p>
  
  <p>From forms.py</p>
  
  <pre><code>class ModifyTeamForm(forms.Form):
  
      action = ChoiceField(choices=[('remove', 'Remove users'), ('promote', 'Promote to lead.')])
  
  
  
      def __init__(self, *args, **kwargs):
  
          # The project to get the team for
          project_id = kwargs.pop('project_id', None)
  
          super(ModifyTeamForm, self).__init__(*args, **kwargs)
  
          project = Project.objects.get(pk=project_id)
  
          # Team for this project
          team = User.objects.filter(groups__name=project.project_name)
  
          # Create a form field to select current team members
          current_team = MultipleChoiceField(required=True, choices = team, widget=CheckboxSelectMultiple)
  
          # Add the field
          self.fields['current_team'] = current_team
  </code></pre>
  
  <p>My views.py</p>
  
  <pre><code>@login_required
  def team(request, project_id): 
  
      if request.method == "POST": 
          # Not yet implemented
          return
      else: 
          form = ModifyTeamForm(project_id=project_id)
  
          template = loader.get_template('projects/team.html')
  
          context = RequestContext(request, {
              'form': form,
          })
  
          return HttpResponse(template.render(context))
  </code></pre>