[PATCH] Make git-format-patch's signoff option more consistent

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>

git-format-patch-script

@@ -6,7 +6,7 @@
 . git-sh-setup-script || die "Not a git archive."
 
 usage () {
-    echo >&2 "usage: $0"' [-n] [-o dir] [--mbox] [--check] [--sign] [-<diff options>...] upstream [ our-head ]
+    echo >&2 "usage: $0"' [-n] [-o dir] [--mbox] [--check] [--signoff] [-<diff options>...] upstream [ our-head ]
 
 Prepare each commit with its patch since our-head forked from upstream,
 one file per patch, for e-mail submission.  Each output file is
@@ -46,7 +46,7 @@ do
     date=t author=t mbox=t ;;
     -n|--n|--nu|--num|--numb|--numbe|--number|--numbere|--numbered)
     numbered=t ;;
-    -s|--s|--si|--sig|--sign)
+    -s|--s|--si|--sig|--sign|--signo|--signof|--signoff)
     signoff=t ;;
     -o=*|--o=*|--ou=*|--out=*|--outp=*|--outpu=*|--output=*|--output-=*|\
     --output-d=*|--output-di=*|--output-dir=*|--output-dire=*|\
@@ -179,9 +179,12 @@ Date: '"$ad"
 
 	test "$signoff" = "t" && {
 		offsigner=`git-var GIT_COMMITTER_IDENT | sed -e 's/>.*/>/'`
-		echo
-		echo "Signed-off-by: $offsigner"
-		echo
+		line="Signed-off-by: $offsigner"
+		grep -q "^$line\$" $commsg || {
+			echo
+			echo "$line"
+			echo
+		}
 	}
 
 	echo '---'