Like being able to change the volume, seek position etc. via
AppleScript, this commit allows you to change the audio desync in ms.

Example:
tell application "VLC"
  -- set audio desync to 0
  set audio desync to -2250
  get audio desync
end tell
Signed-off-by: Boy van Amstel <boy@boyvanamstel.nl>
Signed-off-by: Felix Paul Kühne <fkuehne@videolan.org>