title: django.core.exceptions.ImproperlyConfigured: AUTH_USER_MODEL refers to model 'auth.User' that has not been installed
body: <p>After migrating my django and userena packages like below</p>
  
  <blockquote>
    <p>Django 1.8  to Django 1.9.7</p>
    
    <p>django-userena 1.4.1 to django-userena==2.0.1</p>
  </blockquote>
  
  <p>After running the project , I am getting below this error </p>
  
  <pre><code>Unhandled exception in thread started by &lt;function wrapper at 0xb689641c&gt;
  Traceback (most recent call last):
  File "/home/Documents/environments/venv/local/lib/python2.7/site-packages/django/utils/autoreload.py", line 226, in wrapper
  fn(*args, **kwargs)
  File "/home/Documents/environments/venv/local/lib/python2.7/site-packages/django/core/management/commands/runserver.py", line 116, in inner_run
  self.check(display_num_errors=True)
  File "/home/Documents/environments/venv/local/lib/python2.7/site-packages/django/core/management/base.py", line 426, in check
  include_deployment_checks=include_deployment_checks,
  File "/home/Documents/environments/venv/local/lib/python2.7/site-packages/django/core/checks/registry.py", line 75, in run_checks
  new_errors = check(app_configs=app_configs)
  File "/home/Documents/environments/venv/local/lib/python2.7/site-packages/django/core/checks/urls.py", line 13, in check_url_config
  return check_resolver(resolver)
  File "/home/Documents/environments/venv/local/lib/python2.7/site-packages/django/core/checks/urls.py", line 23, in check_resolver
  for pattern in resolver.url_patterns:
  File "/home/Documents/environments/venv/local/lib/python2.7/site-packages/django/utils/functional.py", line 33, in __get__
  res = instance.__dict__[self.name] = self.func(instance)
  File "/home/Documents/environments/venv/local/lib/python2.7/site-packages/django/core/urlresolvers.py", line 417, in url_patterns
  patterns = getattr(self.urlconf_module, "urlpatterns", self.urlconf_module)
  File "/home/Documents/environments/venv/local/lib/python2.7/site-packages/django/utils/functional.py", line 33, in __get__
  res = instance.__dict__[self.name] = self.func(instance)
  File "/home/Documents/environments/venv/local/lib/python2.7/site-packages/django/core/urlresolvers.py", line 410, in urlconf_module
  return import_module(self.urlconf_name)
  File "/usr/lib/python2.7/importlib/__init__.py", line 37, in import_module
  __import__(name)
  File "/home/Documents/swamy/sample_project/july/5/sample11/sampleapp/urls.py", line 28, in &lt;module&gt;
  (r'^grappelli/', include('grappelli.urls')),
  File "/home/Documents/environments/venv/local/lib/python2.7/site-packages/django/conf/urls/__init__.py", line 52, in include
  urlconf_module = import_module(urlconf_module)
  File "/usr/lib/python2.7/importlib/__init__.py", line 37, in import_module
  __import__(name)
  File "/home/Documents/environments/venv/local/lib/python2.7/site-packages/grappelli/urls.py", line 8, in &lt;module&gt;
  from .views.switch import switch_user
  File "/home/Documents/environments/venv/local/lib/python2.7/site-packages/grappelli/views/switch.py", line 18, in &lt;module&gt;
  User = get_user_model()
  File "/home/Documents/environments/venv/local/lib/python2.7/site-packages/django/contrib/auth/__init__.py", line 155, in get_user_model
  "AUTH_USER_MODEL refers to model '%s' that has not been installed" % settings.AUTH_USER_MODEL
  </code></pre>
  
  <p>django.core.exceptions.ImproperlyConfigured: AUTH_USER_MODEL refers to model 'auth.User' that has not been installed</p>
  
  <p>Here are INSTALLED_APPS in my settings file,</p>
  
  <pre><code>'grappelli.dashboard',
  'grappelli',
  'filebrowser',     
  'django.contrib.admindocs',
  'django.contrib.admin',
  'django.contrib.auth',    
  'django.contrib.contenttypes',
  'django.contrib.sessions',
  'django.contrib.messages',
  'django.contrib.sites',
  'django.contrib.staticfiles',  
  'django.contrib.redirects',
  'django.contrib.sitemaps',
  'haystack',  
  'memcache_status',   
  'stheme',    
  'home',
  'customers',
  'orders',
  #'legacy',
  'products',
  'bloglets',
  'utils',
  'catax',
  'sqls',
  'quotes',    
  #'django_stylus',
  #'djgrid',
  #'obdjects',
  'quickpages', 
  'loginas',
  #'pyjade',
  'django_countries',  
  'debug_toolbar',
  'djide',
  #'dbtemplates',  
  #'aloha',  # out temporarily, migrate to alternate https://github.com/ntucker/django-aloha-edit - JJW
  'coffeescript',
  'django_wysiwyg',
  #'django_bfm',
  'userena',
  'guardian', 
  #'apps',  
  #'filer',
  'easy_thumbnails', 
  'taggit',
  #'taggit_templatetags',
  # 'social_auth',    
  'social.apps.django_app.default', 
  #'socialregistration',
  #'socialregistration.contrib.linkedin',
  'email_extras',
  #'csvimport', 
  'csvimport.app.CSVImportConf',  
  'django_extensions',
  'webshell',
  'easy_select2',  
  #'plata',
  #'plata.contact', 
  #'plata.discount',
  #'plata.payment',
  #'plata.shop',
  'lastmodule',
  </code></pre>
  
  <p>I guess there are some changes in python apps.But I can't find the reason... Does anyone help to fix this issue ?</p>
  
  <p>Thanks In Advance !</p>