Do not crash on *every* page load if there is no ToS Document.
'tos' ReferenceProperty might be present, but still be None.
Patch by: Todd Larsen
Review by: to-be-reviewed
"""Multi-consumer multi-producer dispatching mechanism
Originally based on pydispatch (BSD) http://pypi.python.org/pypi/PyDispatcher/2.0.1
See license.txt for original license.
Heavily modified for Django's purposes.
"""
from django.dispatch.dispatcher import Signal