If the source repository was packed, and git-local-fetch needed to
fetch a pack file, it spewed a misleading error message about not
being able to find the unpacked object. Fixed by adding the
warn_if_not_exists argument to copy_file(), which controls printing
of error messages in case the source file does not exist.
Signed-off-by: Sergey Vlasov <vsu@altlinux.ru> Signed-off-by: Junio C Hamano <junkio@cox.net>