在Go中设置App Engine上下文

I post JSON to an app I registered at Google App Engine but I am baffled by the authentication process in my Go code to get it working in appengine:

func init() {
    http.HandleFunc("/post", handler)
}

func handler(w http.ResponseWriter, r *http.Request) {

    app := appengine.NewContext(r)
    client := &http.Client{
        Transport: &oauth2.Transport{
            Source: google.AppEngineTokenSource(app, "https://www.googleapis.com/auth/bigquery"),
            Base: &urlfetch.Transport{
                Context: app,
            },
        },
    }
    log.Print(client)
}

In following the docs, I have reduced my problem to the code above which consistently gives me the following error:

2015/01/28 09:05:32 appengine: NewContext passed an unknown http.Request

I'd love some pointers as to how I can provide appengine with a "known" http.Request because ultimately I am trying to get to the storage api which also requires a valid context.

Does removing and re go getting google.golang.org/appengine from your GOPATH fixes the issue ?

Edit: Also, a colleague of mine said that after rebooting all went well.