Update: the changes committed on r62269 and r62279 were incorrect and 
reverted in r62292.

Log:
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.

The reworked patch fixes test_getargs2.py, such that it verifies Long() 
and Int() can't be used as indexes.  It also fixes the handling of 'n' 
in getargs.c's convertsimple().  Committed in r62462.