Issue 2440: revert r62269 and r62279.  These changes were made in an effort to fix test_args2.Signed_TestCase.test_n(), which was failing on Windows x64 on the following line:  'self.failUnlessEqual(99, getargs_n(Long()))'.  Although the two commits *did* fix the test on Windows x64, it's become clear that it's the test that's incorrect, and the changes to PyNumber_Index() in particular were not warranted (and actually violate PEP 357).  This commit will get us back to where we were at r62268, before I started butchering things.