Use unauthorized error type for recent

I don't think this will solve **all** of the current problems we're seeing with the cli not refreshing the user's access token when loggregator returns us a 401, but using this same consistent error type for the return value will definitely help users of this library.

Also, I noticed that some very thoughtful developers, namely @jmtuley and @ajackson, implemented more intelligent reading of the HTTP response body  in the case of HTTP fallback that doesn't include a hardcoded buffer size. This seems like a clear win, but I was unsure if a test for this behavior would be reasonable or just bloat.