Manage selection function for Function field

ModelView automatically adds missing RPC definition for selection function but
only for Selection or Reference field. It should also do the same for Function
field which mimic such fields.

issue5903
review30531002

trytond/model/modelview.py

@@ -179,7 +179,10 @@ class ModelView(Model):
 
         # Update __rpc__
         for field_name, field in cls._fields.iteritems():
-            if isinstance(field, (fields.Selection, fields.Reference)) \
+            if (isinstance(field, (fields.Selection, fields.Reference))
+                    or (isinstance(field, fields.Function)
+                        and isinstance(field._field,
+                            (fields.Selection, fields.Reference)))) \
                     and not isinstance(field.selection, (list, tuple)) \
                     and field.selection not in cls.__rpc__:
                 instantiate = 0 if field.selection_change_with else None