Fix scope lookup for unscoped entities
As scope_logic is now always set (since r1250), we need to check if
it is None, rather than check if it exists.
Patch by: Sverre Rabbelier
"""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