Since git-commit-script has a "--signoff" option, use that in
git-format-patch-script, too (and since partial option names are
supported,"--sign" is still valid).
Also, if the message already contains the S-O-B line, silently ignore the
"--signoff" request.
Signed-off-by: Johannes Schindelin <Johannes.Schindelin@gmx.de> Signed-off-by: Junio C Hamano <junkio@cox.net>