Merge r686540, r686541, r686542, r686547 from trunk:

* Note further env variables and that their documentation can be found
  in mod_proxy_http.

* Write variable in lowercase.

* Fix error in default setting for ProxyTimeout

Submitted by: rpluem
Reviewed by: rpluem


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@686548 13f79535-47bb-0310-9956-ffa450edef68