title: Pylint complains about method 'data_received' not overridden, for RequestHandler
body: <p>For example:</p>
  <pre><code>class MainHandler(tornado.web.RequestHandler):
      def get(self):
          self.render('data.html', items = [])
  </code></pre>
  <p>It yields the following Pylint error:</p>
  <blockquote>
  <p>warning (W0223, abstract-method, MainHandler) Method 'data_received' is abstract in class 'RequestHandler' but is not overridden</p>
  </blockquote>
  <p>I understand that somehow it wants me to override this <code>data_received</code> method, but I do not understand why, and what it is for?</p>