The type and special identifying attributes for unbound methods were

removed in Python 3.x, which has proved difficult to deal with, as we're

not always able to correctly determine what the owner might be (or at

all, in the case of classes locally defined within other functions). For

those that do sort of have an owner we can look up, we won't always get

the right one, either, depending on the qualifying name of the method.
We now accept passing an explicit owner= to spy_on(), which will be

used for unbound methods. The owner's value is checked for

compatibility, and errors are raised if incompatible owners are provided

(with suitable messages depending on the function type and

circumstances).
Failing to pass an owner will, at the very least, log a warning for the

caller to see in the event that a unit test fails, even on Python 2.x.

This is to help prepare people to transition to Python 3.x. Going

forward, we recommend always passing an owner for unbound methods.

Unit tests pass.
Used this in some new unit tests that had issues with determining

unbound method owners on Python 3.