* mandos (Client.enable): Bug fix: Start new immediate checker last to
avoid race condition.
(Client.disable): Optionally do not log message.
(ClientDBus.disable): Do not log message if no signal should be sent.
(string_to_delta): More informative error message.
(main.cleanup): Emit D-Bus "ClientRemoved" signal for all clients.
Do not emit any other signal. Move to after
"mandos_dbus_service" is defined.