HTTP Improvements

1) There's no need to use urllib2 for multipart post - use the OAuth2 Client, to be more consistent with the other GET/POST methods.

2) Improve HTTP logging. In particular, don't clutter the logfile with multipart file contents.

3) If the OpenPhoto JSON response can't be decoded, use the HTTP response code instead. This gives a much more sane error message in the case of a 404.