Prevent "git-commit -a path1 path2..."

When you want to create a partial commit, giving -a by mistake
would ignore the given path.  Prevent it.

Signed-off-by: Junio C Hamano <junkio@cox.net>

git-commit.sh

@@ -92,10 +92,13 @@ tt*)
 esac
 
 case "$all,$#" in
-t,*)
+t,0)
 	git-diff-files --name-only -z |
 	git-update-index --remove -z --stdin
 	;;
+t,*)
+	die "Cannot use -a and explicit files at the same time."
+	;;
 ,0)
 	;;
 *)