Python 3.6 made some changes to how methods are executed and how unbound

methods are converted into bound methods. This led to some breakages

when spying on methods containing list comprehensions (and likely other

generators) and when spying on unbound methods. In the former, directly

accessing arguments passed to the function didn't work (but using

locals() was fine), and in the latter the unbound function stayed

unbound on instances (due to attempting to clone and re-set unbound

methods). In some cases, though, locals() didn't at all work.
Now, on Python 3.x, we check both places. If the parameter is in

locals(), we'll use that. Otherwise, we fall back on the actual

argument. This seems to catch all instances that we've hit.
We also no longer try to clone unbound methods at all, fixing

compatibility on all versions.

Unit tests pass on Python 2.7 and 3.4 through 3.6.