title: Find text in gtk.TextView
body: <p>I have a <code>gtk.Textview</code>. I want to find and select some of the text in this <code>TextView</code> programmatically. 
  I have this code but it's not working correctly.</p>
  
  <pre><code>search_str =  self.text_to_find.get_text()
  start_iter =  textbuffer.get_start_iter() 
  match_start = textbuffer.get_start_iter() 
  match_end =   textbuffer.get_end_iter() 
  found =       start_iter.forward_search(search_str,0, None) 
  if found: 
     textbuffer.select_range(match_start,match_end)
  </code></pre>
  
  <p>If the text is found, then it selects all the text in the <code>TextView</code>, but I need it to select only the found text.</p>