#3 updating artist field keeps old artist

[Kjetil Thuen]

If a song has had its artist field updated, the old
artist is still connected to the song. Say you have a
song by "ole ivars", but the tag says "ol ivars". If
you correct the error and run the register routines,
the song will now be credited to both "ol ivars" and
"ole ivars". ole ivars might not like that..