Optionally allow the usage of django-configurations
Document that pytest-django can use django-configurations
Move the django-configurations importer to later on

* Prevents pre-emptive importation of Django
Add tests for the django-configuration integration
Fix test to pass the args seperately
Ensure we install a new enough version of django-configurations
Skip django-configurations tests on Python 2.4/2.5
Merge pull request #32 from dstufft/django-configurations

Support for django-configurations - thanks Donald Stufft!