title: INSTALLED_APPS error in mongoengine code
body: <p>I was working on Django 1.3.1 with mongodb. </p>
  
  <p>I installed following:</p>
  
  <blockquote>
    <p>django-bootstrap-toolkit==2.5.6 django-email-extras==0.1.8
    django-forms-builder==0.7.15 django-pagination==1.0.7</p>
    
    <p>django-grappelli==2.4.2 docutils==0.9.1 python-memcached==1.48
    sphinx-me==0.1.2 wsgiref==0.1.2 django-rte==0.4.0</p>
  </blockquote>
  
  <p>Suddenly I got following error. Any help .</p>
  
  <p>File "/usr/local/lib/python2.7/dist-packages/django_mongodb_engine-0.4.0-py2.7.egg/django_mongodb_engine/<strong>init</strong>.py", line 13, in 
      settings.INSTALLED_APPS.insert(0, 'django_mongodb_engine')
  AttributeError: 'tuple' object has no attribute 'insert'</p>
  
  <p>I tried to convert INSTALLED_APPS as list instead of tuple, but it does not worked .</p>