network disk cache does not take into account the HTTP Vary header

if e.g. a response contains "Vary: Accept" this means that the returned representation depends on the Accept header. A request with a different Accept header will create a different response at the server side, and because of that the cache could return an invalid resource.
In other words, the cache should only return the resource if the list of fields in the "Vary" header in the cached request are the same as the request the cache is about to serve from.