Since git-gc now always calls prune, even with --auto, unreferenced objects
may be removed by more operations than just git-gc. This is important for
clones created using --shared or --reference.
Signed-off-by: Brandon Casey <casey@nrlssc.navy.mil> Signed-off-by: Dmitry Potapov <dpotapov@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>