Sort discs as integers, not strings

[mcvayokay]

For large disc collections (in my particular case, a classical box set with 13 discs), disc numbers are sorted as strings instead of integers. This results in a disc ordering of 1, 10, 11, 12, 13, 2, 3, ...

Presumably this is a simple change, as track numbers do not have this problem. I would try to make the change myself if I knew where to apply it; at a glance it isn't clear. Using version 0.4.6-4eacc22.

[anonbeat]

For now label them as 01 02 03... this is what I do

[mcvayokay]

That's not a great solution for those of us who tag our entire libraries with an automated tool like MusicBrainz Picard. Every time I refresh tags with the latest MusicBrainz database I'll have to go relabel the discs.