core: Improve error message where client's request-line exceeds LimitRequestLine

PR 54384

trunk patch: http://svn.apache.org/r1433613
Submitted by: jailletc36
Reviewed by: minfrin, jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1481512 13f79535-47bb-0310-9956-ffa450edef68