Fix for "wrong auth token" issue in BoxHTTPRequestBuilders.

I found an issue with BoxHTTPRequestBuilders - when there is no saved/logged in user an attempt to issue an upload request gives success in return by default. It wasn't checking the case of "wrong auth token"(it could happen if a nil user is passed or saved auth token is invalid).
I fixed it plus added some tests to make sure that the behavior is correct.

Hope you'll find it useful.