title: Start PyGTK cellrenderer edit from code
body: <p>I have a treeview with an editable CellRendererText:</p>
  
  <pre><code>self.renderer = gtk.CellRendererText()
  self.renderer.set_property('editable', True)
  </code></pre>
  
  <p>But now I need to launch the edition from code instead from user, this is to focus the user attention in the fact he just created a new row and needs to be named. I tried this but does not work:</p>
  
  <pre><code>self.renderer.start_editing(
      gtk.gdk.Event(gtk.gdk.NOTHING),
      self.treeview,
      str(index),
      gtk.gdk.Rectangle(),
      gtk.gdk.Rectangle(),
      0)
  </code></pre>
  
  <p>Neither does not throw errors, but the documentation about for what is each argument is not clear, in fact I really don't know if start_editing method is for this.</p>
  
  <p>All suggestions are welcome, thanks.</p>