void silc_sftp_open(SilcSFTP sftp,
                        const char *filename,
                        SilcSFTPFileOperation pflags,
                        SilcSFTPAttributes attrs,
                        SilcSFTPHandleCallback callback,
                        void *context);

    Open a file indicated by the `filename' with flags indicated by the
    `pflags', and with attributes indicated by the `attsr'.  Calls the
    `callback' to return the opened file handle.