Merge r561456, r561463, r561477, r561485, r561797 from trunk:

Explicitly mention how to do rewriting in a vhost.

PR: 36506


Document that PT implies L.

PR: 40046


Docuemnt the x- headers added by mod_proxy_http.

PR: 41097


Document some -D magic.

PR: 41148


A couple small fixes suggested by Vincent.



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@561800 13f79535-47bb-0310-9956-ffa450edef68