move rfc1413 code to a new module "metadata:mod_ident".

The rfc1413 code itself is mostly c&p, but can still bear
some rework ...

This patch removes the global ap_rfc1413 function and the
ap_rfc1413_timeout variable. It also introduces a new config
directive IdentityCheckTimeout (default 30 sec).

Reviewed by: Justin Erenkrantz


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@98320 13f79535-47bb-0310-9956-ffa450edef68