HttpGet getRedirectURL() == null

With the following code, `getResponseHeader("Location")` returns the redirect URL, but `getRedirectURL()` returns null.

```
HttpGet get = new HttpGet(url, false);  // don't follow redirects
get.run();
log.info("response code: " + get.getResponseCode());  // 302
log.info("location: " + get.getResponseHeader("Location"));  // url
log.info("location: " + get.getRedirectURL());  // null
```