Merge r764239 from trunk:

* Check more strictly that the backend follows the AJP protocol.

Submitted by: mturk
Reviewed by: rpluem, jim, jfclere


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@768507 13f79535-47bb-0310-9956-ffa450edef68