* scd/app.c (notify_cond): New condition variable.
(app_send_devinfo, app_wait): New.
(scd_update_reader_status_file): Kick NOTIFY_COND.
(initialize_module_command): Initialize NOTIFY_COND.
* scd/command.c (struct server_local_s):  Add watching_status.
(cmd_devinfo): New.
(register_commands): Add DEVINFO command.
(send_client_notifications): Write status change to DEVINFO channel.
* scd/scdaemon.h (app_wait, app_send_devinfo): New.