Add ConditionalGetMiddleware to sandbox settings
Add ConditionalGetMiddleware to sandbox settings

This sets the Content-Length response header which is required for
CloudFront and possible other cdn's

sasha0/django-oscar,solarissmoke/django-oscar,django-oscar/django-oscar,sasha0/django-oscar,sonofatailor/django-oscar,django-oscar/django-oscar,sasha0/django-oscar,sonofatailor/django-oscar,sonofatailor/django-oscar,sonofatailor/django-oscar,solarissmoke/django-oscar,sasha0/django-oscar,django-oscar/django-oscar,django-oscar/django-oscar,solarissmoke/django-oscar,solarissmoke/django-oscar