title: generating plural forms into a .pot file
body: <p>I'm internationalizing a python program and cant get plural forms into the .pot file.  I have marked string that require plural translations with a _pl() eg.</p>
  
  <p><code>self.write_info(_pl("%(num)d track checked", "%(num)d tracks checked",
                       song_obj.song_count) % {"num" : song_obj.song_count})</code></p>
  
  <p>Then I'm running:
  <code>xgettext --language=Python --keyword=_pl --output=output.pot *.py</code>
  Only the first (singular) string is generated in the pot file.</p>