cmd/go: show $GOPATH in 'go env' output
cmd/go: show $GOPATH in 'go env' output

Also, sort output.

R=golang-dev, patrick, dave, iant
CC=golang-dev, patrick
http://codereview.appspot.com/6446064

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