All of the remaining tests that had as status of PARSE rather than PASS had
good reasons for not passing the render-and-reparse step: the correct parse tree is
badly formed, so when it is rendered out as HTML, the result doesn't parse into the
same tree. So add them to the list of tests where that step is skipped.

Also, I discovered that it is possible to end up with HTML elements (not just text)
inside a raw text element through reparenting. So change the rendering routines to
handle that situation as sensibly as possible (which still isn't very sensible, but
this is HTML5).

R=nigeltao
CC=golang-dev
https://golang.org/cl/6446137