compat/w32pthreads: add return value to pthread_cond_init().
lavu: add thread message API.
ffmpeg: use thread message API.
Merge remote-tracking branch 'cigaes/master'

* cigaes/master:
  ffmpeg: use thread message API.
  lavu: add thread message API.
  compat/w32pthreads: add return value to pthread_cond_init().

Merged-by: Michael Niedermayer <michaelni@gmx.at>