* thunar/thunar-tree-model.c, thunar/thunar-tree-model.h,

	  thunar/thunar-tree-view.c: Instead of unloading folders
	  when their ref count is zero, we schedule a tree cleanup when
	  a row is collapsed. The reason is simple: the reffing the
	  treeview does is weird which results in glitches when scrolling
	  a large tree.
	  Also added some extra debug code.

(Old svn revision: 28946)