- more precise message for the "force-dolby-surround" option
  - don't use -1 as a value in an integer list option (dangerous casts
    in the wxWidgets interface)
+ modules/audio_filter/converter/a52tofloat32.c:
  - option to disable the internal upmixing algorithm
+ modules/audio_filter/channel_mixer/headphone.c:
  - option to partially compensate the delay introduced by the algorithm
  - option to accept raw Dolby Surround encoded streams