Fix git-format-patch -s to include a Signed-off-by: line...

In the last round of bug fixes the signed-off-by line was still be
generated but it was not including a signed-off-by line :(

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>

git-format-patch.sh

@@ -178,7 +178,7 @@ my ($signoff_pattern, $done_header, $done_subject, $signoff_seen,
     $last_was_signoff);
 
 if ($signoff) {
-	$signoff = `git-var GIT_COMMITTER_IDENT`;
+	$signoff = "Signed-off-by: " . `git-var GIT_COMMITTER_IDENT`;
 	$signoff =~ s/>.*/>/;
 	$signoff_pattern = quotemeta($signoff);
 }