If you use git-p4 with the "--prepare-p4-only" option, then
it prints the p4 command line to use. However, the command
line was incorrect: the changelist specification must be
supplied on standard input, not as an argument to p4.
Signed-off-by: Luke Diamand <luke@diamand.org> Acked-by: Pete Wyckoff <pw@padd.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>