Merge commit 'e57c4706e969afa1f2384481b955ccd9494cddb5'

Merge commit 'e57c4706e969afa1f2384481b955ccd9494cddb5'

* commit 'e57c4706e969afa1f2384481b955ccd9494cddb5':
  lavc: don't reuse audio buffers

This commit causes a 0.5% speedloss for mp3 and 2% for raw pcm, that is
"time ffmpeg" style tested thus includes disk IO, demux and parsing

I would not have merged it if it wasnt required for the "new" buffer API
but sadly it is.
Once the new API is in ill reimplement proper buffer reuse, which will
fix this speedloss. In case we choose not to merge the "new" buffer
API then this commit here should be reverted.

Conflicts:
	libavcodec/internal.h
	libavcodec/utils.c

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