F-Spot's Tag TreeView

I recently fixed up F-Spot's tag TreeView. Right clicking on or dragging several tags used to be practically impossible, and there was no way to make a tag toplevel (having no parent tags) with DnD.
Reparenting two tags to Banff I put the code for the right click/dragging fixes (most of which came straight out of the nautilus code, thanks!) into a reusable TreeView subclass in case others are in need. If you haven't used F-Spot for a while (or haven't yet discovered this feature), you might notice you can make the icons next to your tags smaller now (or even turn them off). That feature has been in since early March, courtesy of Stephane.