Abstract idea of Song instead of pure file management

[Jud Craft]

Matching by analysis alone also has the following caveat:  it breaks
the explicit album distinction.

The exact song may have several releases on different albums
(re-releases, compilations, etc).  To have a user try to say "My OGG
song is from Album Re-release 2008" and Amarok says "No, it clearly
matches an MP3 you have from Album Original Release 2004, I'll put it
there" would be counter-intuitive.

That's why I think the matching should rely on tags first, and then
deep audio comparison later if necessary.