Added methods to search a QueryNode tree for values of a given type either
Added methods to search a QueryNode tree for values of a given type either

* src/Libraries/Hyena/Hyena.Query/QueryNode.cs: Added methods to search
  a QueryNode tree for values of a given type either by depth or
  breadth.

* src/Core/Banshee.Services/Banshee.SmartPlaylist/SmartPlaylistSource.cs:
  Consume the new QueryNode.SearchForValues method.

svn path=/trunk/banshee/; revision=3363

dufoli/hyena,GNOME/hyena,petejohanson/hyena,GNOME/hyena,petejohanson/hyena,arfbtwn/hyena,arfbtwn/hyena,dufoli/hyena