api: update next.txt

Ton of FreeBSD syscall constants.

R=golang-dev, minux.ma
CC=golang-dev
https://codereview.appspot.com/7476046
net/http: add a test verifying header case preservation

Fixes issue 5022

R=golang-dev, minux.ma
CC=golang-dev
https://codereview.appspot.com/7712043