Given how long I've been using the threading module without realising it
does the same thing, I'm actually prepared to live with the wrapper
functions rather than messing with this so close to release.

As Fredrik noted in the python-dev thread, the threading versions of
these are already explicitly documented as being factory functions
rather than classes (and as a reference to _thread.allocate_lock,
threading.Lock has good reason to be a factory function rather than a
class), so it may be appropriate to do the same thing for multiprocessing.