Our usual style when working with subdirectories is to chdir
inside a subshell or to use "git -C", which means we do not
have to constantly return to the main test directory. Let's
convert this old test, which does not follow that style.
Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>