Only do keepalives (and keep state on the connection record) if this request

is the top-level page.

Do not pass If-XXX-Since headers to the r-proxied server on a subrequest,
and we can't handle a 30X response


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@92022 13f79535-47bb-0310-9956-ffa450edef68