However, fixing it so far *appears* to fix a bunch of shy FileStorage
pack[Now]WhileWriting test failures whose connection to loadBefore()
isn't obvious.  It's plausible that it's a real fix for those, just
not (yet) compelling.  It seems very likely to be a real fix for very
rare failures that have shown up only in ChrisM's overnight testrunner
reports (because those did have stuff related to loadBefore() in their
tracebacks).