For my 64-bit Linux system running with GCC 4.4.3-fc12-whatever, you
can't do 'printf("%lld", (int64_t)x);' Instead you need to tell the
compiler 'printf("%lld", (long long int)x);' or else it doesn't
believe the types match.  This is why we added U64_PRINTF_ARG; it
looks like we needed an I64_PRINTF_ARG too.