pacman-key: display the unsupported command to the user

If the user provides an unsupported command, inform the user that this
switch is unknown, display usage and exit.

Signed-off-by: Ivan Kanakarakis <ivan.kanak@gmail.com>
Signed-off-by: Dan McGee <dan@archlinux.org>

scripts/pacman-key.sh.in

@@ -321,5 +321,6 @@ case "${command}" in
 	-V|--version)
 		version; exit 0 ;;
 	*)
+		error "$(gettext "Unknown command:") $command"
 		usage; exit 1 ;;
 esac