bug#13429: 24.2; `window-end' returns point after last point in window

[Eli Zaretskii <eliz@gnu.org>]

> From: Nathan Trapuzzano <nbtrap@nbtrap.com>
> Date: Sun, 13 Jan 2013 17:12:59 -0500
> 
> The current doc-string for `window-end' states that the function returns
> the ``position at which display currently ends in WINDOW''. I understand
> this to mean, more or less, the greatest position visible in
> WINDOW.

This interpretation is incorrect.

> For example, when a given window is displaying a buffer that overflows
> the window, a call to `window-end' will return the greatest visible
> position **plus one**.

This is what is meant by "position at which display ends".
Suggestions for how to describe that better are welcome.

> Whereas, when the buffer does not overflow the window
> (i.e., when the window displays the end of the buffer, including any
> blank lines at the end), `window-end' returns just the greatest visible
> position, the same thing that `point-max' would return.

This is still consistent: there's no character at position returned by
point-max.  The last position visible in the window is one less that
the returned value in this case as well.