Merge r1775195 from trunk:

http_header_filter: on check_headers() failure, use AP_FILTER_ERROR and EOC
semantics to respectively warn the caller and cleanly terminate the connection
afterwards.

Suggested by: rpluem


Submitted by: ylavic
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1775828 13f79535-47bb-0310-9956-ffa450edef68