fastcgi: sync fastcgi_params with upstream fastcgi.conf

This is a risky change for `SCRIPT_FILENAME` but it handles more
situation than fastcgi_params. Upstream still ships the previous
fastcgi_params file.

Fixes: #499 

As explained in #499, the change is disruptive. I am doing the pull request for comments only. Only `SCRIPT_FILENAME` is changed (and `HTTPS` a bit).