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.