2.5 and 2.4 are in security-fix-only mode, so we don't set them in
versions since bugs won't get fixed there.

I don't think overridden methods should be called, since that would slow
down attribute lookup, which is already a bottleneck in Python.  Whether
there should be an error message is a more complicated question, and I'd
have to look at how this is implemented to even have an opinion on that.