Fix a couple of bugs exposed by the new __index__ code. The 64-bit buildbots

Fix a couple of bugs exposed by the new __index__ code.  The 64-bit buildbots
were failing due to inappropriate clipping of numbers larger than 2**31
with new-style classes. (typeobject.c)  In reviewing the code for classic
classes, there were 2 problems.  Any negative value return could be returned.
Always return -1 if there was an error.  Also make the checks similar
with the new-style classes.  I believe this is correct for 32 and 64 bit
boxes, including Windows64.

Add a test of classic classes too.