BUG: Disable check for oldstyle classes in python3

backport of #3885
Merge pull request #3899 from juliantaylor/py3-info-1.7

backport PR #3885 to 1.7.x
Ensure NotImplemented is passed on in MaskedArray ufunc's
Add test cases to ensure NotImplemented is passed on
Small corrections to tests
Merge pull request #3904 from charris/backport-1.7-3900

Backport 1.7 3900