bug#14825: 24.3.50; split-window-below miscounts window lines

[martin rudalics]

> To reproduce:
>
>   emacs -Q
>   Click S-mouse-1 and select "Change Buffer Font"
>   Under "Size" type 6 and click OK
>
> You should now have *scratch* buffer displayed with a very small font
>
>   Hit RET 5 times to have a 10-line buffer
>   C-x 2
>   C-u 10 C-x ^
>
> You should now have 2 windows displaying *scratch*, the lower one about
> 10 lines tall.
>
>   C-x o
>   C-x 2
>    => Window #<window 0x3817df0 on *scratch*> too small for splitting
>
> But that window is 10 lines tall, while the minimum window height is 4
> lines, so I would expect Emacs to honor the request and produce 2
> windows.  And indeed, if I do the same with a 10-line window without
> making the font smaller, the window is split.

I attached a patch that tries to fix this scenario.  Please have a
look.

Thanks, martin

split-window-below.diffs
Description: Text document