Jesse, how much (if any) of the rest of the package will work without
the synchronize module? If it isn't a lot, then it may be a matter of
just making this a cleaner ImportError and an expected test suite skip
on OpenBSD and FreeBSD.

(Unfortunately, our OpenBSD and FreeBSD buildbots are so unreliable that
they don't get much attention when they go red - it looks to me like the
OpenBSD buildbot isn't even managing to build _multiprocessing at the
moment, because HAVE_SEM_OPEN is incorrectly set to 1).