Xiph: support TRACKNUMBER=xx/xx in vorbis comments

Yeah, yeah, such a clever idea, thx...
Let' not use TRACKTOTAL or TOTALTRACKS or TOTALTRACK or TRACKSTOTAL,
because you know, there is not enough options...
Oh, and let's not make ANY of the above official in the spec, because
then, people could follow the spec...
https://www.xiph.org/vorbis/doc/v-comment.html

Next time, please use mkv...
Map Voxware MetaSound Codec IDs
GLwin32: fix init crash

Regression from 5989169 and ticket #7558

Close #9124
Contribs: update Opus to 1.0.3
Contribs: update freetype to 2.5.0.1
Contribs: update ZVBI (!) to 0.2.34
aout: rework aout_Interleave()

This no longer assumes that planes are contiguous. It should help with
libav reference counting, and also avoids interleaving unused padding.
Contribs: update libpng to 1.6.3
avcodec: avoid forward declaration
avcodec: refer to AVFrame as a pointer, non-functional change
avcodec: use reference counting for audio decoding
configure: no deprecated libav features in use
extras/tools: update libtool
extras/tools: update automake
Fix sizeof mismatch
zpl: Fix memory leaks
qt4: fix memory leaks
mpeg_ts: fix potential array off by one
hotkeys: Fix test (was always true)
Fix use of uninitialized variable (cid #1049012)