bug#17644: 24.4.50; provide access to all mode-line lighters (e.g. those from C code)

[Drew Adams]

>     (setq mode-line-modes
>           (cl-nsubstitute '(:eval (when (buffer-narrowed-p) " DREW"))
>                           "%n"
>                           mode-line-modes
>                           :test 'string=
>                           :key (lambda (e) (when (stringp e) e))))

Good; thx.  I didn't realize there was a separate % construct
just for `Narrow'.

Is `Narrow' the only such "abnormal" lighter implemented in C?
If so then I will close this bug.  Thx.