Patch 2

This should fix the issue for [this Google Groups post](https://groups.google.com/forum/?fromgroups=#!topic/django-non-relational/NA02zAqCktw).  

Was causing:

File "/usr/local/lib/python2.7/dist-packages/django_mongodb_engine-0.4.0-py2.7.egg/django_mongodb_engine/__init__.py", line 13, in <module> 
    settings.INSTALLED_APPS.insert(0, 'django_mongodb_engine') 
AttributeError: 'tuple' object has no attribute 'insert'