generate_tar() eventually calls write_tar_archive() which does all the
"real" work and which also calls git_config(git_tar_config). We only
need to do this once.
Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx> Signed-off-by: Junio C Hamano <junkio@cox.net>