code: static function parseDateTime($apiDateTimeString)
      {
          $dt = \DateTime::createFromFormat(self::$dateTimeFormat, $apiDateTimeString);
          if ($dt === false) throw new Exception_BadResponse(
              "Bad date/time from server: ".Util::q($apiDateTimeString));
          return $dt;
      }
docs: Parses date/time strings returned by the Dropbox API.  The Dropbox API returns date/times
  formatted like: `"Sat, 21 Aug 2010 22:31:20 +0000"`.
  
  @param string $apiDateTimeString
  A date/time string returned by the API.
  
  @return \DateTime
  A standard PHP `\DateTime` instance.
  
  @throws Exception_BadResponse
  Thrown if `$apiDateTimeString` isn't correctly formatted.