cmd/godoc: don't link unexported identifiers
cmd/godoc: don't link unexported identifiers

R=golang-dev, gri, gri
CC=golang-dev
https://codereview.appspot.com/9722045

Committer: Robert Griesemer <a6752097faebf1f02d80107d77a9be009089afe3@golang.org>

wesolows/golang-old,wesolows/golang,wesolows/golang,firebitsbr/golang-old,wesolows/golang,firebitsbr/golang-old,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang,wesolows/golang-old,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang,wesolows/golang-old,wesolows/golang,wesolows/golang-old,wesolows/golang,firebitsbr/golang-old,wesolows/golang-old,firebitsbr/golang-old