Code review comment for lp:~encukou/picard/move-complete-album-only

(as seen on mailing list:)
I've started using Picard, and I really like how I can make a clean collection
directory with the Move Files option. But then I clicked Save on an incomplete
album, which made a bit of a mess there. I think a "Move complete albums only"
option would be nice.
So here's a patch for it :)