add missing keystore
use existing keystore
398285 - ProxyServlet mixes cookies from different clients.

Now ProxyServlet's HttpClient uses HttpCookieStore.Empty, so it never stores cookies.
Avoid copying sensitive headers when copying a Request.
Completed the implementation of DeferredContentProvider.

DeferredContentProvider is used to provide content after
Request.send(...) is called, a use case that is useful
in SPDY-to-HTTP proxies, where content arrives in SPDY
data frames at later times than the headers.
398285 - ProxyServlet mixes cookies from different clients.

Now ProxyServlet's HttpClient uses HttpCookieStore.Empty, so it never stores cookies.