Fixed #14656 -- Atom1Feed should write atom:published element

https://code.djangoproject.com/ticket/14656

The first commit – e51e589728208e856734958e7115e0b26ab6e55d was some [housekeeping](http://programmer.97things.oreilly.com/wiki/index.php/The_Boy_Scout_Rule) because I was in the neighbourhood… if it's cluttering the history I'll remove it. Cheers. :monkey_face: