The only thing that has substansively changed is that Go 1.8 handles
redirect logic more safely than previous versions. This means we can
drop our special handling to avoid following redirects to other
domains. We were only doing that to protect against the possibility
of leaking auth headers. With Go 1.8, the auth headers are not
forwarded when following a redirect to another domain, so we don't
need our special handling any more.

As long as people are attempting to build with the Makefile, the new
check_go_version script should cause the build to stop if our
collaborators aren't using at least version 1.8 of go.