Since commit d96855f (merge-base: teach "--fork-point" mode, 2013-10-23)
we can replace a shell loop in git-pull with a single call to
git-merge-base. So let's do so.
Signed-off-by: John Keeping <john@keeping.me.uk> Signed-off-by: Junio C Hamano <gitster@pobox.com>