hostname: Test and log useragent_host per-request across various modules,

including the scoreboard, expression and rewrite engines, setenvif,
authz_host, access_compat, custom logging, ssl and REMOTE_HOST variables.
PR55348  [William Rowe]

This is the complete change set which applies cleanly to 2.4.x as well,
the server/scoreboard.c will follow, which does not apply due to drift.



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1729930 13f79535-47bb-0310-9956-ffa450edef68