title: PySide popup showing list and multiple select
body: <p>I am programming a GUI using PySide. I currently have the user select a directory with many data files in it. I load these filenames into a list. I would like the GUI to display a popup menu showing the list of filenames allowing the user to select one, many or all the files to proceed. Right now I am using,</p>
  
  <pre><code>items, ok = QInputDialog.getItem(self, "Select files", "List of files", datafiles, 0, False)
  </code></pre>
  
  <p>This only lets the user select one file, and not multiple. How can I show the user a list of items and have them highlight as many as they want and then return the list?</p>
  
  <p>Thanks!</p>