title: django filer - ImportError: cannot import name mixins
body: <p>I have a django 1.4 installation and I have django-cms running.
  I'm try to install filer but when I syncdb or runserver I keep having this error.</p>
  
  <pre><code> from filer.models import mixins
   ImportError: cannot import name mixins
  </code></pre>
  
  <p>In my setting.py I have:</p>
  
  <pre><code>INSTALLED_APPS = (
  'django.contrib.auth',
  'django.contrib.contenttypes',
  'django.contrib.sessions',
  'django.contrib.sites',
  'django.contrib.messages',
  'django.contrib.staticfiles',
  # Uncomment the next line to enable the admin:
  'django.contrib.admin',
  'cms', 
  'mptt',
  'menus', 
  'south',
  'sekizai', 
  'ftlom',
  #'cms.plugins.text',
  #'cms.plugins.picture',
  'cmsplugin_twitter',
  'easy_thumbnails',
  'filer',
  #'ordered_model',
  #'cmsplugin_filer_file',
  #'cmsplugin_filer_folder',
  'cmsplugin_filer_image',
  #'cmsplugin_gallery',
  'cms.plugins.video',
  #'gunicorn',
  
  
  # Uncomment the next line to enable admin documentation:
  # 'django.contrib.admindocs',
  </code></pre>
  
  <p>)</p>
  
  <p>If I remove filer and all its plugins my site works fine. What could possibly cause the problem? thanks</p>
  
  <p>Traceback :</p>
  
  <pre><code>Validating models...
  
  Unhandled exception in thread started by &lt;bound method Command.inner_run of     &lt;django.contrib.staticfiles.management.commands.runserver.Command object at 0x1050d4fd0&gt;&gt;
  Traceback (most recent call last):
  File "/Users/Alex/.virtualenvs/FTLOM/lib/python2.7/site-   packages/django/core/management/commands/runserver.py", line 91, in inner_run
  self.validate(display_num_errors=True)
  File "/Users/Alex/.virtualenvs/FTLOM/lib/python2.7/site-packages/django/core/management/base.py", line 266, in validate
  num_errors = get_validation_errors(s, app)
  File "/Users/Alex/.virtualenvs/FTLOM/lib/python2.7/site-packages/django/core/management/validation.py", line 30, in get_validation_errors
  for (app_name, error) in get_app_errors().items():
  File "/Users/Alex/.virtualenvs/FTLOM/lib/python2.7/site-packages/django/db/models/loading.py", line 158, in get_app_errors
  self._populate()
  File "/Users/Alex/.virtualenvs/FTLOM/lib/python2.7/site-packages/django/db/models/loading.py", line 67, in _populate
  self.load_app(app_name)
  File "/Users/Alex/.virtualenvs/FTLOM/lib/python2.7/site-packages/django/db/models/loading.py", line 88, in load_app
  models = import_module('.models', app_name)
  File "/Users/Alex/.virtualenvs/FTLOM/lib/python2.7/site-packages/django/utils/importlib.py", line 35, in import_module
  __import__(name)
  File "/Users/Alex/.virtualenvs/FTLOM/lib/python2.7/site-packages/filer/models/__init__.py", line 2, in &lt;module&gt;
  from filer.models.clipboardmodels import *
  File "/Users/Alex/.virtualenvs/FTLOM/lib/python2.7/site-packages/filer/models/clipboardmodels.py", line 5, in &lt;module&gt;
  from filer.models import filemodels
  File "/Users/Alex/.virtualenvs/FTLOM/lib/python2.7/site-packages/filer/models/filemodels.py", line 8, in &lt;module&gt;
  from filer.models import mixins
  </code></pre>
  
  <p>ImportError: cannot import name mixins</p>
  
  <p>This my pip freeze :</p>
  
  <pre><code>Django==1.4
  PIL==1.1.7
  South==0.8.1
  cmsplugin-filer==0.9.5
  cmsplugin-twitter==1.0.4
  django-classy-tags==0.4
  django-cms==2.4.1
  django-filer==0.9.3
  django-mixins==0.0.10
  django-mptt==0.5.2
  django-ordered-model==0.2.0
  django-polymorphic==0.5
  django-sekizai==0.7
  easy-thumbnails==1.3
  gunicorn==17.5
  html5lib==1.0b1
  six==1.3.0
  wsgiref==0.1.2
  </code></pre>