gst/ffmpegcolorspace/: Added AYUV colorspace and handle RGBA a bit more respectful.

gst/ffmpegcolorspace/: Added AYUV colorspace and handle RGBA a bit more respectful.

Original commit message from CVS:
* gst/ffmpegcolorspace/avcodec.h:
* gst/ffmpegcolorspace/gstffmpegcodecmap.c:
(gst_ffmpeg_pixfmt_to_caps), (gst_ffmpeg_caps_to_pixfmt),
(gst_ffmpegcsp_avpicture_fill):
* gst/ffmpegcolorspace/gstffmpegcolorspace.c:
(gst_ffmpegcsp_caps_remove_format_info):
* gst/ffmpegcolorspace/imgconvert.c: (avpicture_get_size),
(shrink12), (img_get_alpha_info), (deinterlace_line),
(deinterlace_line_inplace):
* gst/ffmpegcolorspace/imgconvert_template.h:
Added AYUV colorspace and handle RGBA a bit more respectful.