support for vendored code?

[ryanking]

We have a monorepo (one repo many projects) that uses vendoring. I've gotten the tool to the point of working, but it can never find any of the vendored code. Example error:

/Users/rk/go/hail/src/services/api/handlers/add_credit_card_handler_test.go:8:4: could not import github.com/onsi/ginkgo (cannot find package "github.com/onsi/ginkgo" in any of:
    /usr/local/Cellar/go/1.6.2/libexec/src/github.com/onsi/ginkgo (from $GOROOT)
    /Users/rk/go/hail/src/github.com/onsi/ginkgo (from $GOPATH))

That code is at /Users/rk/go/hail/src/vendor/github.com/onsi/ginkgo, which should be found if vendoring is turned on.