pack-objects: be incredibly anal about stdio semantics

This is the "letter of the law" version of using fgets() properly in the
face of incredibly broken stdio implementations.  We can work around the
Solaris breakage with SA_RESTART, but in case anybody else is ever that
stupid, here's the "safe" (read: "insanely anal") way to use fgets.

It probably goes without saying that I'm not terribly impressed by
Solaris libc.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>