Fix AttributeError in CheckPrivilegeNode.render

In the update from 0.1.0a to 0.1, registration code was refactored from __init__.py to registration.py, but privileges_tags was not updated.  

When rendering a template using the check_privilege tag, Django would throw an AttributeError.
Merge pull request #1 from jacobwegner/master

Fix AttributeError in CheckPrivilegeNode.render