Fix HTML issues

• missing /article/xhtml entirely

This looks like a URL_Rewrite issue, since the link does not end up on the 404 page, but redirects to /articles.

• code parsing issues on the following

  • accessibility-whack-a-mole
  • motion-with-meaning-semantic-animation-in-interface-design
  • good-designers-good-clients
  • amoreuseful404
  • sandbags
  • daemonskin
  • dom

All these articles (one of them is a column) contain HTML errors that cause libxml2 to fail parsing the main-content <div> properly.

Detailed description of issue here, with massive thanks to @hrbrmstr for helping diagnose the problem.

• Ask for help on Twitter: done
• Ask for help here: @zeldman @alistapart @murtaugh @mkammerer