ext/ffmpeg/gstffmpegcodecmap.c: Add ALAC, shorten and some more in new FFMPEG snapshot of 21/4, somewhere this aftern...

Original commit message from CVS:
* ext/ffmpeg/gstffmpegcodecmap.c: (gst_ffmpeg_codecid_to_caps),
(gst_ffmpeg_caps_with_codecid), (gst_ffmpeg_caps_to_codecid),
(gst_ffmpeg_get_codecid_longname):
Add ALAC, shorten and some more in new FFMPEG snapshot of
21/4, somewhere this afternoon.
* ext/ffmpeg/gstffmpegdec.c: (gst_ffmpegdec_register):
* ext/ffmpeg/gstffmpegenc.c: (gst_ffmpegenc_register):
Add warnings to decoder registration to easier add new ones
during snapshot updates.