enhance the CGI scripting support so that script can take path parameters. That is, a script at /cgi/foo is called when the request path is /cgi/foo/bar/... This commit also introduce some backward incompatible changes as the default env variables set for the CGI script changed.

change the meaning of the -x flag: now it takes a string and executes CGI scripts only if they are inside a directory with the given name, relatively to the document root.

or SIGUSR2 for poor peoples

don’t stop-the-world-until-cgi-end, but rather poll on the script, so we can handle other requests in the meantime.