go.tools/go/types: handle embedded interfaces in NewInterface
go.tools/go/types: handle embedded interfaces in NewInterface

R=gri
CC=golang-dev
https://codereview.appspot.com/39040043

Committer: Robert Griesemer <a6752097faebf1f02d80107d77a9be009089afe3@golang.org>

t-yuki/go.tools.old,t-yuki/go.tools.old,t-yuki/go.tools.old