GtkTreeStore/GtkListStore/GInterface/GtkTreeModel support

[Andy Wingo]

Hey kids,

I coded up some support for the tree/list widgets in Gtk 2. I even
worked out support for GtkTreeModels implemented in Scheme, as is done
in PyGtk; see examples/gtk/tree-model.scm for more details. I'm working
on making a framework for guile-gtk-demo (like gtk-demo and pygtk-demo),
but I'm not quite finished yet.

So, check it out and see if I forgot a file again ;)

Regards,

wingo.