rev-parse: fix using "--default" with "--verify"

rev-parse: fix using "--default" with "--verify"

Before this patch, something like:

$ git rev-parse --verify HEAD --default master

did not work, while:

$ git rev-parse --default master --verify HEAD

worked.

This patch fixes that, so that they both work (assuming
HEAD and master can be parsed).

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>