Correct infinite loop with the same location

The issue is apparent when loading from Google Drive (e.g. `https://dd7777360edd06ed6fa7cbc0725dbd736cbda015.googledrive.com/host/0B9Vee7pZ81xmUzBqUmluT3FWVkU/my.js`). The root cause is that the `304 Not Modified` responds with a location header, which results in an infinite loop to the same url. This patch only does a redirect now if the url has changed.