ext/ffmpeg/: Sync with gst-plugins ffmpegcolorspace, align-by-4. Ready to re-sync gst-plugins ffmpegcolorspace with o...

Original commit message from CVS:
* ext/ffmpeg/gstffmpegcodecmap.c: (gst_ffmpeg_avpicture_fill):
* ext/ffmpeg/gstffmpegcodecmap.h:
* ext/ffmpeg/gstffmpegcolorspace.c: (gst_ffmpegcsp_chain):
* ext/ffmpeg/gstffmpegdec.c: (gst_ffmpegdec_get_buffer),
(gst_ffmpegdec_chain):
* ext/ffmpeg/gstffmpegenc.c: (gst_ffmpegenc_chain_video):
Sync with gst-plugins ffmpegcolorspace, align-by-4. Ready to
re-sync gst-plugins ffmpegcolorspace with ours and deprecate
this one.