Merge r1730723 from trunk:

Add 451... Needed to adjust RESPONSE_CODES which
was not in the provided patch
BUGZ# 58985
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1748212 13f79535-47bb-0310-9956-ffa450edef68