lib: recreate aout when module is changed

libvlc_audio_output_set() had no practical effects as the audio output
was consistently created before the application had the opportunity to
select a non-default module. This fixes it.

An alternative would be to remove the function entirely. Exposing
module names to LibVLC applications is bad design.

lib/audio.c

@@ -130,6 +130,7 @@ int libvlc_audio_output_set( libvlc_media_player_t *mp, const char *psz_name )
     var_SetString( mp, "aout", value );
     free( value );
 
+    vlc_player_aout_Reset(mp->player);
     return 0;
 }