Nice work!  Seems like we're going to be able to look forward to faster 
integer arithmetic in Python 2.7 / 3.1.  I'll try to find time to review 
your patch properly sometime soon.

Regarding the HAVE_INT64, there's a standard autoconf macro 
AC_TYPE_INT64_T (and its unsigned counterpart AC_TYPE_UINT64_T) that 
automatically sets int64_t (or uint64_t) to a 64-bit (unsigned) integer 
type whenever it exists.  So don't worry about the preprocessor stuff for 
the moment, so long as it's working on your machine;  we can fix it in 
Python's configure script instead sometime.