Original commit message from CVS:
* gst/matroska/matroska-demux.c:
(gst_matroska_demux_parse_metadata_id_simple_tag):
* gst/matroska/matroska-ids.h:
* gst/matroska/matroska-mux.c: (gst_matroska_mux_write_simple_tag):
Add some more tags, improve debugging a bit and make sure that
GValue transformation has succeeded before using the result
as a tag.