There were two problems with detection and handling of class methods as call targets in Python 3:
* Methods no longer define `im_self` -- this is now only `__self__`
* The `types` module no longer defines a `ClassType`
The universally-compatible (v2.6+) solution was to switch to using the `inspect` module -- whose interface has been stable -- and to checking the method attribute `__self__`.
(It doesn't hurt that `inspect` checks are more brief and we now no longer need the `types` module here.)
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