bug#17554: 24.3.91; [Regression] re-usage of dired *Marked Files* buffer window

[martin rudalics]

> Maybe Martin has better ideas?

The earlier behavior was handwoven and allowed three windows to coexist
simultaneously on one and the same frame.  We can't achieve that via
`display-buffer' because the default value of `split-height-threshold'
precludes it.  IMHO that value is ridiculously small and in practice
always inhibits popping up a third window.  But changing that value for
the release doesn't sound like a good idea to me.

So IIUC we have to write our own `split-window-preferred-function' here.
Unless anyone has a better idea ...

martin