correctly handle an abnormal fastcgi termination. httpd handles the

correctly handle an abnormal fastcgi termination.  httpd handles the
disconnection from the fastcgi application via server_file_error which
assumes that the reply was completey done.  However, if the fastcgi
reply wasn't complete (e.g. because slowcgi hit the timeout) the HTTP
client are left "hanging" and waiting for a reply until they give up.

This adds a server_fcgi_error callback to handle the "no headers" and
"incomplete data" cases and properly close the reply before falling back
to server_file_error.

OK claudio@