Added basic support for OPTIONS and TRACE HTTP methods:

Added basic support for OPTIONS and TRACE HTTP methods:
 - New parser function client_max_forwards which decrements
   the Max-Forwards HTTP header field of OPTIONS and TRACE
   requests by one before forwarding
 - New parser function client_host which extracts the host
   and port information from the HTTP header field if the
   request URI was not absolute
 - Don't crumble and re-add the Host: header, but only generate
   and append if missing