title: How to resolve "django.core.exceptions.ImproperlyConfigured: Application labels aren't unique, duplicates: foo" in Django 1.7?
body: <p>On upgrading to Django 1.7 I'm getting the following error message from <code>./manage.py</code></p>
  
  <pre><code>$ ./manage.py 
  Traceback (most recent call last):
    File "./manage.py", line 16, in &lt;module&gt;
      execute_from_command_line(sys.argv)
    File "/home/johnc/.virtualenvs/myproj-django1.7/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 427, in execute_from_command_line
      utility.execute()
    File "/home/johnc/.virtualenvs/myproj-django1.7/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 391, in execute
      django.setup()
    File "/home/johnc/.virtualenvs/myproj-django1.7/local/lib/python2.7/site-packages/django/__init__.py", line 21, in setup
      apps.populate(settings.INSTALLED_APPS)
    File "/home/johnc/.virtualenvs/myproj-django1.7/local/lib/python2.7/site-packages/django/apps/registry.py", line 89, in populate
      "duplicates: %s" % app_config.label)
  django.core.exceptions.ImproperlyConfigured: Application labels aren't unique, duplicates: foo
  </code></pre>
  
  <p>What's the problem and how do I resolve it?</p>