[#28] Test for Vary headers
[#28] Test for Vary headers

http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.44
http://www.w3.org/Protocols/rfc2616/rfc2616-sec13.html#sec13.6

alphagov/cdn-acceptance-tests,alphagov/cdn-acceptance-tests,mikepea/cdn-acceptance-tests,alphagov/cdn-acceptance-tests,mikepea/cdn-acceptance-tests,alphagov/cdn-acceptance-tests,mikepea/cdn-acceptance-tests,mikepea/cdn-acceptance-tests