When this option is passed to git p4 clone, the checkout at the end would
previously fail. This patch fixes it by optionally creating the master branch
from refs/heads/p4/master, which is the correct one for this option.
Signed-off-by: Tor Arvid Lund <torarvid@gmail.com> Acked-By: Simon Hausmann <simon@lst.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>