fate: correctly set sample rate for mp2 tests
mpegvideo: operate with pointers to AVFrames instead of whole structs

The most interesting parts are initialization in ff_MPV_common_init() and
uninitialization in ff_MPV_common_end().

ff_mpeg_unref_picture and ff_thread_release_buffer have additional NULL
checks for Picture.f, because these functions can be called on
uninitialized or partially initialized Pictures.

NULL pointer checks are added to ff_thread_release_buffer() stub function.

Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>
Merge commit '60fd7d36c47d62d4c603bf16c213b1a924f5cfcf'

* commit '60fd7d36c47d62d4c603bf16c213b1a924f5cfcf':
  fate: correctly set sample rate for mp2 tests

Conflicts:
	tests/fate/acodec.mak
	tests/lavf-regression.sh

one hunk has been ommited as it breaks fate

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

* qatar/master:
  mpegvideo: operate with pointers to AVFrames instead of whole structs

Conflicts:
	libavcodec/h261dec.c
	libavcodec/h263dec.c
	libavcodec/intrax8.c
	libavcodec/mpeg12enc.c
	libavcodec/mpegvideo.c
	libavcodec/mpegvideo.h
	libavcodec/mpegvideo_enc.c
	libavcodec/mpegvideo_motion.c
	libavcodec/mpegvideo_xvmc.c
	libavcodec/msmpeg4.c
	libavcodec/ratecontrol.c
	libavcodec/vaapi.c
	libavcodec/vc1dec.c
	libavcodec/vdpau_vc1.c

See: fc567ac49e17151f00f31b59030cd10f952612ef
Merged-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/snowenc: remove operations that have become redundant with AVFrame pointers

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/mpegvideo: remove AVFrame padding, as the hack isnt needed anymore

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