Use the same internal model for m2m and o2m

tryton/gui/window/view_form/view/form_gtk/many2many.py

 #This file is part of Tryton.  The COPYRIGHT file at the top level of
 #this repository contains the full copyright notices and license terms.
 import gtk
 from tryton.gui.window.view_form.screen import Screen
 from interface import WidgetInterface
 from one2many import Dialog
 import tryton.rpc as rpc
 from tryton.gui.window.win_search import WinSearch
 from tryton.gui.window.view_form.widget_search.form import _LIMIT
 import tryton.common as common
@@ skipping 148 matching lines @@
             self.screen.display()
             return False
         super(Many2Many, self).display(model, model_field)
         new_models = model_field.get_client(model)
         if self.screen.models != new_models:
             self.screen.models_set(new_models)
         self.screen.display()
         return True
 
     def display_value(self):
-        return self._view.modelfield.rec_name(self._view.model)
+        ids = self._view.modelfield.get_default(self._view.model)
+        try:
+            result = rpc.execute('model', self.attrs['relation'], 'read',
+                    ids, ['rec_name'], rpc.CONTEXT)
+        except:
+            return str(ids)
+        return ', '.join(x['rec_name'] for x in result)
 
     def set_value(self, model, model_field):
         self.screen.current_view.set_value()
         return True