bisect: print an error message when "git rev-list --bisect-vars" fails Before this patch no error was printed when "git rev-list --bisect-vars" failed. This can happen when bad and good revs are mistaken. This patch prints an error message on stderr that describe the likely failure cause. Signed-off-by: Christian Couder <chriscool@tuxfamily.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>