When we disable "Transfer-Encoding: chunked" in the fastcgi backend

When we disable "Transfer-Encoding: chunked" in the fastcgi backend
because we are going to send an empty body we have to provide
"Content-Length: 0" otherwise some browsers (Firefox, Safari) just
hang until httpd(8) closes the connection.
Problem reported by Matthias Pressfreund, debugged with weerd@ who
pointed out that the problem is browser dependent.
OK tracey