Re: mouse-drag-mode-line should maybe use window-tree

[Richard M. Stallman]

    I find I can only move the vertical split to the left or right by
    dragging on the left end of the center-right modeline (at * above).  The
    cursor does change to <=> when hovering over the left end of the
    bottom-right modeline (at o above), but trying to drag with mouse-1 has
    no effect.

I just added a function adjust-window-trailing-edge
which should make it easy to fix this bug.  We just have to change
the Lisp code for sideways dragging.  Where is that?