move h-entry from body to article on single-post pages

this is the final change to make php-mf2 happy. combined with the child theme parts i mentioned in the other pull request, it seems to be parsing ok. here are a couple examples:

single page:
http://pin13.net/mf2/?url=http%3A%2F%2Fsnarfed.org%2F2013-10-23_oauth-dropins

feed:
http://pin13.net/mf2/?url=http%3A%2F%2Fsnarfed.org%2F