go/types: "inherit" type in constant declarations w/o initialization expressions (bug fix)
go/types: "inherit" type in constant declarations w/o initialization expressions (bug fix)

R=adonovan
CC=golang-dev
https://codereview.appspot.com/7060054
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go