title: Forms error - __init__() got an unexpected keyword argument 'prefix'
body: <p>I have 2 forms in one  and i added prefix to separate it in view. But I get error: <strong>__init__() got an unexpected keyword argument 'prefix'</strong></p>
  
  <p>I read documentation about prefix and other issue on stack about it but this doesn't help me.</p>
  
  <p><strong>My view.py:</strong></p>
  
  <pre><code>@user_passes_test(lambda u: u.is_staff, login_url='/account/login/')
  def client_create(request):
      dict = {}
      dict['title'] = 'New client'
  
      if request.method == 'POST':
          form_user = ClientUserCreateForm(request.POST, prefix="test1")
          form_client = ClientCreateForm(request.POST, prefix="test2")
          return HttpResponse(request.POST['first_name'])
          # if form_user.is_valid() and form_client.is_valid():
          #     print(request.POST)
      else:
          dict['form_user'] = ClientUserCreateForm(prefix="test1")
          dict['form_client'] = ClientCreateForm(prefix="test2")
          return render(request, 'panel/client/create.html', dict)
  </code></pre>
  
  <p>I have two forms and they have init and when i remove it from form then prefix work's correct.</p>
  
  <p><strong>My forms.py</strong></p>
  
  <pre><code>class ClientUserCreateForm(forms.ModelForm):
      class Meta:
          model = User
          fields = ('first_name', 'last_name', 'email')
  
      def __init__(self):
          super(ClientUserCreateForm, self).__init__()
          self.fields['first_name'].widget.attrs.update({
              'type': 'text',
              'class': 'form-control',
              'id': 'input-text',
          })
          self.fields['last_name'].widget.attrs.update({
              'type': 'text',
              'class': 'form-control',
              'id': 'input-text',
          })
          self.fields['email'].widget.attrs.update({
              'type': 'text',
              'class': 'form-control',
              'id': 'input-text',
          })
  
  
  class ClientCreateForm(forms.ModelForm):
      country = forms.CharField(max_length=2, widget=forms.Select(
          choices=CountriesShortcut.objects.all().values_list('code', 'name').order_by('id')
      ))
      forwarding_country = forms.CharField(max_length=2, widget=forms.Select(
          choices=CountriesShortcut.objects.all().values_list('code', 'name').order_by('id')
      ))
  
      class Meta:
          model = Client
          fields = ('name', 'vat', 'address', 'zip_code', 'city', 'country', 'forwarding_address',
                    'forwarding_zip_code', 'forwarding_city', 'forwarding_country', 'phone',
                    'mailing_email', 'regon')
  
      def __init__(self):
         super(ClientCreateForm, self).__init__()
          self.fields['name'].widget.attrs.update({
              'type': 'text',
              'class': 'form-control',
              'id': 'input-text',
          })
          self.fields['vat'].widget.attrs.update({
              'type': 'text',
              'class': 'form-control',
              'id': 'input-text',
          })
          (....)
          self.fields['regon'].widget.attrs.update({
              'type': 'text',
              'class': 'form-control',
              'id': 'input-text',
          })
  </code></pre>
  
  <p><strong>Traceback:</strong></p>
  
  <pre><code>Environment:
  
  Request Method: GET
  Request URL: http://127.0.0.1:8000/panel/client/create/
  
  Django Version: 1.8.8
  Python Version: 3.5.1
  Installed Applications:
  ('django.contrib.admin',
   'django.contrib.auth',
   'django.contrib.contenttypes',
   'django.contrib.sessions',
   'django.contrib.messages',
   'django.contrib.staticfiles',
   'core',
   'client',
   'registration',
   'avatar',
   'filer',
   'mptt',
   'easy_thumbnails',
   'reversion',
  'guardian')
  Installed Middleware:
  ('django.contrib.sessions.middleware.SessionMiddleware',
   'django.middleware.common.CommonMiddleware',
   'django.middleware.csrf.CsrfViewMiddleware',
   'django.contrib.auth.middleware.AuthenticationMiddleware',
   'django.contrib.auth.middleware.SessionAuthenticationMiddleware',
   'django.contrib.messages.middleware.MessageMiddleware',
   'django.middleware.clickjacking.XFrameOptionsMiddleware',
   'django.middleware.security.SecurityMiddleware')
  
  
  Traceback:
  File "C:\Users\loc\dJangoEnvironment\lib\site-packages\django\core\handlers\base.py" in get_response
    132.                     response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "C:\Users\loc\dJangoEnvironment\lib\site-packages\django\contrib\auth\decorators.py" in _wrapped_view
    22.                 return view_func(request, *args, **kwargs)
  File "C:\Users\loc\PycharmProjects\CRM\core\views.py" in client_create
    72.         dict['form_user'] = ClientUserCreateForm(prefix="test1")
  
  Exception Type: TypeError at /panel/client/create/
  Exception Value: __init__() got an unexpected keyword argument 'prefix'
  </code></pre>
  
  <p><strong>Traceback 2 - after update __init__:</strong></p>
  
  <pre><code>Environment:
  
  Request Method: GET
  Request URL: http://127.0.0.1:8000/panel/client/create/
  
  Django Version: 1.8.8
  Python Version: 3.5.1
  Installed Applications:
  ('django.contrib.admin',
   'django.contrib.auth',
   'django.contrib.contenttypes',
   'django.contrib.sessions',
   'django.contrib.messages',
   'django.contrib.staticfiles',
   'core',
   'client',
   'registration',
   'avatar',
   'filer',
   'mptt',
   'easy_thumbnails',
   'reversion',
   'guardian')
  Installed Middleware:
  ('django.contrib.sessions.middleware.SessionMiddleware',
   'django.middleware.common.CommonMiddleware',
   'django.middleware.csrf.CsrfViewMiddleware',
   'django.contrib.auth.middleware.AuthenticationMiddleware',
   'django.contrib.auth.middleware.SessionAuthenticationMiddleware',
   'django.contrib.messages.middleware.MessageMiddleware',
   'django.middleware.clickjacking.XFrameOptionsMiddleware',
   'django.middleware.security.SecurityMiddleware')
  
  
  Traceback:
  File "C:\Users\loc\dJangoEnvironment\lib\site-packages\django\core\handlers\base.py" in get_response
    132.                     response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "C:\Users\loc\dJangoEnvironment\lib\site-packages\django\contrib\auth\decorators.py" in _wrapped_view
    22.                 return view_func(request, *args, **kwargs)
  File "C:\Users\loc\PycharmProjects\CRM\core\views.py" in client_create
    73.         dict['form_client'] = ClientCreateForm(prefix="test2")
  File "C:\Users\loc\PycharmProjects\CRM\core\forms.py" in __init__
    75.         super(ClientUserCreateForm, self).__init__(*args, **kwargs)
  
  Exception Type: TypeError at /panel/client/create/
  Exception Value: super(type, obj): obj must be an instance or subtype of type
  </code></pre>