title: ImportError: cannot import name AccessMixin
body: <p>I'm trying to run the following package from github - <code>https://github.com/rollstudio/django-admin2-sb</code></p>
  
  <p>But I'm getting the following traceback</p>
  
  <pre><code>Traceback (most recent call last):
    File "manage.py", line 10, in &lt;module&gt;
      execute_from_command_line(sys.argv)
    File "/usr/local/lib/python2.7/dist-packages/django/core/management/__init__.py", line 385, in execute_from_command_line
      utility.execute()
    File "/usr/local/lib/python2.7/dist-packages/django/core/management/__init__.py", line 354, in execute
      django.setup()
    File "/usr/local/lib/python2.7/dist-packages/django/__init__.py", line 21, in setup
      apps.populate(settings.INSTALLED_APPS)
    File "/usr/local/lib/python2.7/dist-packages/django/apps/registry.py", line 85, in populate
      app_config = AppConfig.create(entry)
    File "/usr/local/lib/python2.7/dist-packages/django/apps/config.py", line 87, in create
      module = import_module(entry)
    File "/usr/lib/python2.7/importlib/__init__.py", line 37, in import_module
      __import__(name)
    File "/usr/local/lib/python2.7/dist-packages/djadmin2/__init__.py", line 13, in &lt;module&gt;
      from . import core
    File "/usr/local/lib/python2.7/dist-packages/djadmin2/core.py", line 14, in &lt;module&gt;
      from . import apiviews
    File "/usr/local/lib/python2.7/dist-packages/djadmin2/apiviews.py", line 12, in &lt;module&gt;
      from .viewmixins import Admin2Mixin
    File "/usr/local/lib/python2.7/dist-packages/djadmin2/viewmixins.py", line 15, in &lt;module&gt;
      from braces.views import AccessMixin
  ImportError: cannot import name AccessMixin
  </code></pre>
  
  <p>braces is installed I can see it in the following location - </p>
  
  <p><code>/usr/local/lib/python2.7/dist-packages/braces/views</code></p>
  
  <p><code>_access.py</code> contains the class <code>class AccessMixin(object):</code></p>
  
  <p>so why doesn't it import?</p>