Merge r1635762 from trunk:

Support custom ErrorDocuments for HTTP 501 and 414 status codes.
PR 57167 [Edward Lu <Chaosed0 gmail.com>]

Submitted By: Edward Lu <Chaosed0 gmail.com>
Committed By: covener

Submitted by: covener
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1638071 13f79535-47bb-0310-9956-ffa450edef68