Changed the way the forwarded HTTP headers are computed. Now pazpar2 sends

Changed the way the forwarded HTTP headers are computed. Now pazpar2 sends
the following ones:
- the original 'Host:' header from the web browser request
  Host: flurry:9090
  (notice: not tampering with this one any more, as it did break virtual
   domain configuration in Apache!!)
- some pazpar2 specific version number, listening host
  (from config file proxy/@myurl) and listening port (from config file
   listen/@port)
   pazpar2-version: 0.1
   pazpar2-server-host: flurry.index
   pazpar2-server-port: 9090
- the standard 'Via:' header
  Via: 1.1 flurry.index:9090 (pazpar2/0.1)
- the standard 'X-forward-For' header, containing the true web browser
  client address
  X-Forwarded-For: 10.0.1.66

These changes should make pazpar2 HTTP complient, and allow the backend Apache
server to get the information it needs to be able to do IP based
authentification and such like stuff. Notice that the 'Host:' header is now
passed unchanged, otherwise virtual host setups do not work.