Set PATH_INFO and PATH_TRANSLATED properly for student CGI scripts.
If the requested path doesn't exist, interpretservice now traverses up the directory tree until it finds a prefix of the path that does exist. If we are allowed to execute that path, we do so, giving it the trimmed bits in PATH_INFO. If execution is not permissible, we 404 anyway.
Fixes [ 2094777 ] Serve: Allow path after CGI script