Original commit message from CVS:
Reviewed by:  Ronald S. Bultje  <rbultje@ronald.bitfreak.net>
* gst-libs/gst/tag/tag.h:
Add the MusicBrainz tags and prototype
gst_tag_register_musicbrainz_tags().
* gst/tags/Makefile.am:
Add tags.c.
* gst/tags/tags.c:
Implement gst_tag_register_musicbrainz_tags().
* ext/vorbis/oggvorbisenc.c:
Register the MusicBrainz tags.
* gst/tags/gstvorbistag.c:
Add mapping for MusicBrainz tags. All above fixes #167639.