Factor out the 'key fields without link_id' logic from document
Also make sure the to-be-removed is present before removing it when
doing the field reordening.
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