Return 'real' error status codes instead APR_EGENERAL.

The return status code will be used to determine wether
the message is invalid or the remote host failed processing
the request. This is needed to mark the worker as in
error state in case it is member of load balancer.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@160668 13f79535-47bb-0310-9956-ffa450edef68