* src/audio_output/common.c, include/aout_internal.h: added a new function
   aout_FifoFirstDate() that allows the aout plugin to schedule the first
   play.
* src/audio_output/output.c: fixed another problem affecting the audio quality.
* modules/audio_output/directx.c: improvements. The buffering scheme has been
   changed to be less affected by temporary starving. We also schedule the first   sample to play.