DM-191: Measure and save aperture corrections in SFM

https://jira.lsstcorp.org/browse/DM-191
I also tend to avoid super as
	1.  It's not clear (and requires you to repeat the superclass name)
	2.  It only matters with multiple inheritance (I think)
However
	3.  It's one of the few things that python3 improves, so if we use it now maybe 2to3 will improve our code?

Ask on lsst-data and see what KTL thinks.

						R