The recent work on using string_list to represent the list of refs
that matched with the refs on the other side during fetch heavily
depends on the sort order by string_list's implementation, and
changing string_list will break it. Document that it uses strcmp()
order, at least for now.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu> Signed-off-by: Junio C Hamano <gitster@pobox.com>