set_model method

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class view : tree_view obj ->
...
    method set_model : model option -> unit

and

class entry_completion :
  ([> `entrycompletion|`celllayout] as 'a) Gtk.obj ->
...
    method set_model : GTree.model -> unit

class combo_box :
  ([> Gtk.combo_box] as 'a) Gtk.obj ->
...
    method set_model : GTree.model -> unit

I believe combo_box & entry_completion classes should also have "model
option" as a parameter (you pass None to unset the current model).
This is mentioned in GTK docs:

void gtk_combo_box_set_model (GtkComboBox *combo_box,
                              GtkTreeModel *model);

Sets the model used by combo_box to be model. Will unset a previously
set model (if applicable). If model is NULL, then it will unset the
model.

- Dmitry Bely