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This improves readability a lot and prevent us from reinventing the wheel.

it did not work properly (proper check is impossible without blocking)

Remove the sys/socket.h check. We don't really use it anyway, and socket calls have to be somewhere anyway

modules/services_discovery/sap.c: Don't trust announcement down packet, but support implicit timeout.
* As suggested in the RFC we remove the discovered media if there is no new packet after three average packet period. (implicit timeout).
* Announcement of removal packet can be used to silently replace an announce by an other.
* Add a timeout argument to net_Select.

Now lets hunt the format warnings!

 - Remove net_ListenSingle from LibVLC API
 - Improve error message when network protocol to be used is ambiguous

* update vlc_symbols.h

courmisch, can you please check ?

it was merely a slower (and buggier) recv() nowadays.

The only use of the timeout was to poll b_die, but net_ReadInner()
takes care of that already.