How can I get a 304 from Github?

curl.log

$ curl 'https://github.com/julien51.atom' -I
HTTP/1.1 200 OK
Server: nginx
Date: Tue, 09 Oct 2012 08:23:19 GMT
Content-Type: application/atom+xml; charset=utf-8
Connection: keep-alive
Status: 200 OK
Cache-Control: private, max-age=0, must-revalidate
X-Runtime: 35
X-Frame-Options: deny
Content-Length: 71535
ETag: "49b45badf4e23ce51f927bdd14ffecc3"
Strict-Transport-Security: max-age=2592000

$ curl 'https://github.com/julien51.atom' -I -H'If-None-Match: 49b45badf4e23ce51f927bdd14ffecc3' 
HTTP/1.1 200 OK
Server: nginx
Date: Tue, 09 Oct 2012 08:23:40 GMT
Content-Type: application/atom+xml; charset=utf-8
Connection: keep-alive
Status: 200 OK
ETag: "49b45badf4e23ce51f927bdd14ffecc3"
X-Runtime: 29
Strict-Transport-Security: max-age=2592000
X-Frame-Options: deny
Content-Length: 71535
Cache-Control: private, max-age=0, must-revalidate

$ curl 'https://github.com/julien51.atom' -I -H'If-None-Match: \"49b45badf4e23ce51f927bdd14ffecc3\"' 
HTTP/1.1 200 OK
Server: nginx
Date: Tue, 09 Oct 2012 08:24:03 GMT
Content-Type: application/atom+xml; charset=utf-8
Connection: keep-alive
Status: 200 OK
X-Runtime: 29
Cache-Control: private, max-age=0, must-revalidate
ETag: "49b45badf4e23ce51f927bdd14ffecc3"
X-Frame-Options: deny
Strict-Transport-Security: max-age=2592000
Content-Length: 71535