Just as we have "%(upstream)" to report the "@{upstream}"
for each ref, this patch adds "%(push)" to match "@{push}".
It supports the same tracking format modifiers as upstream
(because you may want to know, for example, which branches
have commits to push).
Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>