compiler: Don't warn for unknown type when importing anonymous field.
compiler: Don't warn for unknown type when importing anonymous field.

R=iant
CC=gofrontend-dev
https://golang.org/cl/14652047

anlhord/gofrontend,anlhord/gofrontend,qskycolor/gofrontend,golang/gofrontend,anlhord/gofrontend,anlhord/gofrontend,golang/gofrontend,qskycolor/gofrontend,anlhord/gofrontend,qskycolor/gofrontend,golang/gofrontend,qskycolor/gofrontend,golang/gofrontend,qskycolor/gofrontend,anlhord/gofrontend,qskycolor/gofrontend,anlhord/gofrontend,qskycolor/gofrontend