Allow 304 cache

Passes on each requests "If-Modified-Since" and "If-None-Match" header to allow "304 Not Modified" responses through the proxy.
This reduces bandwidth and decreases page loading time.

No modifications have been made to admin.php or post.php so if you use the admin page to set your settings you'll lose the allow_304 lines from your settings.php and gain a php notice of 
Notice: Undefined index: allow_304