[mb-style] Covers, jazz and renamed songs.

[Mike Morrison]

I'm just waiting for the DB to include works (compositions), in which case 
the question of covers/versions won't be as big a problem; all recorded 
performances of a composition can link back to the composition itself, and 
"cover" relationships will only be necessary when someone's performance is 
based on a specific performer's previous recording of the composition.

When it comes to renamed songs, perhaps the compositions will be able to 
have alternate names or aliases, and/or some recordings of a song will be 
able to have a different name from the primary name of the work itself.

Mike