html: correctly parse </html> in <head> element.

Pass tests1.dat, test 92:
<head></html><meta><p>

| <html>
|   <head>
|   <body>
|     <meta>
|     <p>

Also pass tests through test 98:
<p><b><div><marquee></p></b></div>

R=nigeltao
CC=golang-dev
https://golang.org/cl/5359054
2 files changed