bug#12170: save-excursion fails boundary case with recenter

[martin rudalics]

>> (1) By "window height", I meant the number of lines displayed for the actual
>> buffer, not counting the mode line or minibuffer.  It turns out this is one
>> less than the value returned by `window-height'.
>
> As documented, window-height returns the height of the window
> including the mode line (and the header line, if there is any).  So
> the above is expected.

To avoid this confusion `window-total-height' should be used instead of
`window-height'.  The "number of lines displayed for the actual buffer"
is returned by the function `window-body-height'.

martin