Modify int8 to not depend on sscanf(), and fix configure's test

Modify int8 to not depend on sscanf(), and fix configure's test
for int8 support.  configure now checks only snprintf() for int8 support,
not sprintf and sscanf as it used to.  The reason for doing this is that
if we are supplying our own snprintf code (which does handle long long int),
we now only need working long long support in the compiler not in the
platform's C library.  I have verified that int8 now passes regression test
on HPUX 9, and I think it should work on SunOS 4.1.* and other older
platforms if gcc is used.