only the relevant items are refreshed, but that all of the tracks for an
album will be refreshed any time a cover image is added or removed for that
album.  (Without reoading the whole collection.)

There's still a weird delay on painting the listview icon when an image is
dragged in (it's updated on the next repaint), but I'll find that later.  It
may be a QListView quirk.

svn path=/trunk/kdemultimedia/juk/; revision=361654