Up to date version that incorporates the BDFL-Pronouncement to use __iadd__ rather than __add_ab__. Also made PyNumber_InPlacePower() a three-argument function (since normal Power() is one, and we can't change this functions' prototype later, if we would want to.) The three argument InPlacePower() does the normal batch of coercions, so it's not terribly likely to remain an 'in-place' operation :-S

I'm working on docs, but on my laptop, not incorporated in this patch. Also, the testcase needs to be expanded a bit, and probably incorporated with the test_class testcase I added last week.