Fix pack-index issue on 64-bit platforms a bit more portably.

Fix pack-index issue on 64-bit platforms a bit more portably.

Apparently <stdint.h> is not enough for uint32_t on OpenBSD; use
"unsigned int" -- hopefully that would stay 32-bit on every
platform we care about, at least until we update the pack-index
file format.

Our sha1 routines optimized for architectures use uint32_t and
expects '#include <stdint.h>' to be enough, so OpenBSD on arm or
ppc might have similar issues down the road, I dunno.

Signed-off-by: Junio C Hamano <junkio@cox.net>