Major changes between hybi-08 and hybi-13
- hybi-08 uses Sec-WebSocket-Origin, but hybi-13 uses Origin
- hybi-13 introduces new close status codes.

hybi-17 spec (editorial changes of hybi-13) mentions
- if a server doesn't support the requested version, it MUST respond
  with Sec-WebSocket-Version headers containing all available versions.
- client MUST close the connection upon receiving a masked frame
- server MUST close the connection upon receiving a non-masked frame
note that hybi-17 still uses "Sec-WebSocket-Version: 13"

see http://code.google.com/p/pywebsocket/wiki/WebSocketProtocolSpec
for changes between spec drafts.

R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/5147043