bug#3142: 23.0.92; split-window-prefered-function should be able to use split-window-horizontally/split-window-vertically

[Juri Linkov]

> That's not obvious!  I like the idea of the split window thresholds,
> but it needs to be a lot more obvious how to use them.  What's wrong
> with my suggestion to change the customize interface to have two more
> options "Always split vertical" and "Always split horizontal" that
> calls the appropriate functions?

I remember we once considered creating a default function with
"intelligently splitting" logic (IOW, moving the `else' part of `if'
in `window--try-to-split-window' to a separate function)
and setting the default value of `split-window-preferred-function'
to the name of this function.

This will allow defining three const values in defcustom:
- the default function name;
- vertically splitting function;
- horizontally splitting function;

- and user-defined function's name.

-- 
Juri Linkov
http://www.jurta.org/emacs/