core: Deal with the widespread use of apr_status_t return values

as HTTP status codes, as documented in PR#31759 (a bug shared by
the default handler, mod_cgi, mod_cgid, mod_proxy, and probably
others).

+1: niq, minfrin, rpluem


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@463488 13f79535-47bb-0310-9956-ffa450edef68