old_contents: import wkhtmltox
  
  img = wkhtmltox.Image()
  img.set_global_setting('out', 'test.pdf')
  img.set_global_setting('in', 'http://www.google.com')
  img.convert()
new_contents: import wkhtmltox
  
  img = wkhtmltox.Image()
  img.set_global_setting('out', 'test.jpg')
  img.set_global_setting('in', 'http://www.google.com')
  img.convert()
  
subject: correct output filename extension