Merge r1553204, r1555240, r1572198 from trunk:

* Do not perform SNI / Host header comparison in case of a forward proxy request as
  in case of a forward proxy request the host header can not be used for virtual
  host selection in our webserver.


* Update comment. No functional change.

* Put a note in CHANGES about r1553204
Submitted by: rpluem
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1573362 13f79535-47bb-0310-9956-ffa450edef68