'Returns the list of relational fields linking to res.users that should
trigger an auto subscribe. The default list checks for the fields
- called \'user_id\'
- linking to res.users
- with track_visibility set
In OpenERP V7, this is sufficent for all major addon such as opportunity,
project, issue, recruitment, sale.
Override this method if a custom behavior is needed about fields
that automatically subscribe users.'

@api.model
def _message_get_auto_subscribe_fields(self, updated_fields, auto_follow_fields=None):

    if (auto_follow_fields is None):
        auto_follow_fields = ['user_id']
    user_field_lst = []
    for (name, field) in self._fields.items():
        if ((name in auto_follow_fields) and (name in updated_fields) and getattr(field, 'track_visibility', False) and (field.comodel_name == 'res.users')):
            user_field_lst.append(name)
    return user_field_lst
