Restore support for the AUTH_HANDLED return code in AUTHN providers,

like in 2.2, which allows authn provider to return their own status
in r->status (custom error code, or return a redirect)



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1499351 13f79535-47bb-0310-9956-ffa450edef68