ac3: update AC3PreferredStereoDownmixMode.

'11b' is reserved in the A/52 specification,
but newer encoders use it to indicate a Dolby
Pro Logic II compatible Lt/Rt downmix.
lavu: add AV_FRAME_DATA_DOWNMIX_INFO side data type.
ac3dec: set AV_FRAME_DATA_DOWNMIX_INFO side data.
Prepare for 10_beta1 Release
Merge commit '9c0e4b3395cad79c560d03d2a94595d89e017885'

* commit '9c0e4b3395cad79c560d03d2a94595d89e017885':
  ac3: update AC3PreferredStereoDownmixMode.

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit 'c98f3169bfb578c1a4e407b44524f0bfa3b4dc0c'

* commit 'c98f3169bfb578c1a4e407b44524f0bfa3b4dc0c':
  lavu: add AV_FRAME_DATA_DOWNMIX_INFO side data type.

Conflicts:
	doc/APIchanges
	libavutil/version.h

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit '9cd4bc41760f8ad879e248920eacbe1e7757152c'

* commit '9cd4bc41760f8ad879e248920eacbe1e7757152c':
  ac3dec: set AV_FRAME_DATA_DOWNMIX_INFO side data.

Conflicts:
	libavcodec/version.h

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge remote-tracking branch 'qatar/master'

* qatar/master:
  Prepare for 10_beta1 Release

Conflicts:
	RELEASE

merge only for metadata

Merged-by: Michael Niedermayer <michaelni@gmx.at>
oggdec/vorbis: fix stream duration condition

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