Document acceptance test (implementation already passes): "If a new cacheable...response is received from a resource while any existing responses for the same resource are cached, the cache SHOULD use the new response to reply to the current request." http://www.w3.org/Protocols/rfc2616/rfc2616-sec13.html#sec13.12
httpcomponents/httpclient/trunk/httpclient-cache/src/test/java/org/apache/http/impl/client/cache/TestProtocolRecommendations.java