xferfcn.py pep8 formatting
xferfcn.py pep8 formatting

Conflicts:
	control/xferfcn.py

Signed-off-by: Clancy Rowley <e705cc08c4ba823aaf7a019236e134509e8d7636@princeton.edu>

murrayrm/python-control,roryyorke/python-control,python-control/python-control