title: howto get the selectionChanged signal
body: <p>Hi I am developing a plugin for Qgis in python, I need to connect the sselectionChanged signal emitted when a feature of the layer is selected, I could not find any examples on internet, here is what I have done as far   </p>
  
  <pre><code>QObject.connect(self.iface.mapCanvas(),SIGNAL("selectionChanged(QgsMapLayer)"), self.test)
  </code></pre>
  
  <p>on the log of qgis  I get this warning    </p>
  
  <pre><code>Warning: Object::connect:  (receiver name: 'MainWindow')
  </code></pre>