ext/taglib/gstid3v2mux.cc: Write GST_TAG_MUSICBRAINZ_DISCID and GST_TAG_CDDA_CDDB_DISCID into ID3v2 TXXX frames (fixe...

Original commit message from CVS:
* ext/taglib/gstid3v2mux.cc: (add_musicbrainz_tag), (add_funcs):
Write GST_TAG_MUSICBRAINZ_DISCID and GST_TAG_CDDA_CDDB_DISCID
into ID3v2 TXXX frames (fixes #347848).