A+C: Jonathan Rudenberg (individual CLA)

Generated by addca.

R=gobot
CC=golang-dev
https://codereview.appspot.com/7700043
net/http: add additional status codes defined in RFC 6585

428 Precondition Required
429 Too Many Requests
431 Request Header Fields Too Large
511 Network Authentication Required

R=golang-dev, bradfitz
CC=golang-dev
https://codereview.appspot.com/7678043

Committer: Brad Fitzpatrick <bradfitz@golang.org>