bug#3598: 23.0.94; doc string of frame-root-window

[martin rudalics]

> Doc string:
> Returns the root-window of frame.
>
> 1. "root-window" should be "root window".
>
> 2. Root window needs to be explained - what is it?
>
> With no explanation, this doc string says nothing at all:
> "`frame-root-window' returns the frame's root window". Gee thanks a
> lot! `thrinblat-oag-plaz' returns the thrinblat's oag plaz.
>
> 3. And the manual's don't help - `frame-root-window' is not mentioned.

IIUC `frame-root-window' was deliberately never described because up to
Emacs 22 it was not always safe to call Lisp functions with an internal
window as argument.  So I think this function was intended for internal
use only.

martin