core (httpcache): PersistentHttpCacheStorage for httpclient-cache
core: basic ProxyServlet
core: removed NullCookieStore
core (ProxyServlet): add header proxying, hop-by-hop header filtering
core (ProxyServlet): proxy query string
core (ProxyServlet): log errors for unhandled HTTP methods
core (ProxyServlet): increase maximum connections
core (HttpCacheTest): test vary header
core (HttpProxy): add setCacheDirectory() method