When hitting 304, ETag, Content-Location, Expires, Cache-control and
Vary should all be sent to the client.

See http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.3.5
for some more details

Thanks to Rogério Schneider for the patch.

Fixes #529



git-svn-id: http://www.varnish-cache.org/svn/branches/2.0@4295 d4fa192b-c00b-0410-8231-f00ffab90ce4