usbmuxd_events_unsubscribe is blocked about 2~3 secs

[yanqinglu]

If users don't install iTunes, the usbmuxd_events_unsubscribe will be blocked about 2~3 secs. usbmuxd_events_unsubscribe calls thread_join to wait the thread to be finished, but the sleep in usbmuxd_listen_poll delay it. Should not use the sleep function, it's better to use a event to wait for timeout, then set the event in usbmuxd_events_unsubscribe .

[yanqinglu]

By the way, the select calling in socket_connect also blocks the usbmuxd_events_unsubscribe