Changes with nginx 0.7.18 13 Oct 2008

    *) Change: the "underscores_in_headers" directive; now nginx does not
       allows underscores in a client request header line names.

    *) Feature: the ngx_http_secure_link_module.

    *) Feature: the "real_ip_header" directive supports any header.

    *) Feature: the "log_subrequest" directive.

    *) Feature: the $realpath_root variable.

    *) Feature: the "http_502" and "http_504" parameters of the
       "proxy_next_upstream" directive.

    *) Bugfix: the "http_503" parameter of the "proxy_next_upstream" or
       "fastcgi_next_upstream" directives did not work.

    *) Bugfix: nginx might send a "Transfer-Encoding: chunked" heaer line
       for HEAD requests.

    *) Bugfix: now accept threshold depends on worker_connections.