[Muine] More multiple artist smartness

[Aaron Gyes <floam sh nu>]

Say I've got an album where all the tracks are by a single artist except
for one. They're all "Person A", then one track is 'Person A and Person
B". Muine will call the album by "Person A and Person A and Person B. I
think Muine should be able to figure this out and just call the album
"By Person A and Person B".

Aaron