PR63628: individual status codes for ProxyErrorOverride.

Support specifying the http status codes to be considered by ProxyErrorOverride 

Submitted By: Martin Drößler <mail martindroessler.de>
Committed By: covener



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1876404 13f79535-47bb-0310-9956-ffa450edef68
