[Nautilus-list] music view should activate automatically now

[Maciej Stachowiak <mjs eazel com>]

The Music view should now automatically be available as a choice in
any directory that contains mp3 files. The old way of explicitly
enabling will still work but should be unnecessary.

Make sure to `killall oafd gconfd' after you make install to see this
since I had to change an oafinfo file to do it.

 - Maciej