[gtkada] Treeview Set_Model

[Arnaud Charlet]

> I've applied the fix, and it works. I just made my treeview updates a
> lot faster. This is useful to know:
> There are no Freeze and Thaw procedures for a treeview, but here is a
> workaround that accomplishes the same:

Indeed. We've also added recently in Gtk.Tree_Store two procedures
Freeze/Thaw_Sort which disables sorting as indicated in this
url.

> http://scentric.net/tutorial/sec-treemodel-add-rows.html#sec-treestore-adding-many-rows