ext/ffmpeg/: debug recurring events at LOG level do some timestamp setting heuristics on the pcache, with the net res...

Original commit message from CVS:

* ext/ffmpeg/gstffmpegcodecmap.c: (gst_ffmpeg_codecid_to_caps),
(gst_ffmpeg_smpfmt_to_caps):
* ext/ffmpeg/gstffmpegdec.c: (gst_ffmpegdec_setcaps),
(gst_ffmpegdec_negotiate), (gst_ffmpegdec_frame),
(gst_ffmpegdec_chain):
debug recurring events at LOG level
do some timestamp setting heuristics on the pcache, with the
net result of having more buffers have approximately correct
timestamps.
This allows playback of h263/3gp files taking fps from the demuxer,
which before always set GST_CLOCK_TIME_NONE as timestamp.