setup_revisions sets a variety of flags based on the setting of other
flags, such as setting the limited flag when topo_order is set. To avoid
circumventing any invariants created by setup_revisions, we set
revs.topo_order before calling it rather than after.
Signed-off-by: Elijah Newren <newren@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>