go spec: adjust language for constant typing
go spec: adjust language for constant typing

Fixes issue 1421.

R=r, rsc, iant, ken2
CC=golang-dev
http://codereview.appspot.com/4039042
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go