Do not include attributes which are inherited.
Also some extra comments.
Review URL: http://codereviews.googleopensourceprograms.com/1603
"""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