They stopped working in version 2.0 and never made much sense.

This will replace the "audio-device" variable that was hard-coded into
audio output plugins.

Instead of busy waiting and retrying, buffer packets and wait for the next
pf_play() call to write them to the sound card.
We now have 2 linked lists:
    - packets not accepted yet by Enqueue()
    - packets accepted by Enqueue(), not yet written to hardware, and
    waiting to be released in PlayedCallback()

This work has been sponsored by Sergio Ammirata.

This is off by default due to being more CPU/memory intensive.
Closed Captions can only be read in 10 bits mode.

Ref #5686

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>