Update the attributes of self.widget based on self.flagged.

def update_w(self):
        """Update the attributes of self.widget based on self.flagged.
        """
        if self.flagged:
            self._w.attr = 'flagged'
            self._w.focus_attr = 'flagged focus'
        else:
            self._w.attr = 'body'
            self._w.focus_attr = 'focus'