bug#16909: 24.3; scrolling *Completions* window with tab sometimes chooses a wrong window

[martin rudalics <rudalics@gmx.at>]

 >> (1) Kill the *Completions* buffer when we're done so it won't be
 >>     inadvertently displayed by `other-window-for-scrolling'.
 >
 >
 > How is this supposed to work?
 > The problem is _during_ the Completions buffer is shown, when we're hitting
 > Tab, not when we're done. Besides its window is usually closed
 > automatically.

We have to detect the moment when the window is closed automatically
anyway.  At that time we can either kill the buffer or reset
`other-window-scroll-buffer'.

 > Killing the buffer won't make the scroll-other-window work
 > the usuall way.

How comes?  Ahh... I see.  If `other-window-scroll-buffer' is non-nil
and the buffer was killed in the meantime `display-buffer' throws an
arg out of range error.  That's silly ... should be fixed now.

 >> (2) Bind `other-window-scroll-buffer' temporarily only as long as the
 >>     *Completions* buffer is shown.
 >
 >
 > This would work I imagine. But don't do this in general when the
 > Completions buffer is shown, but only when we use autocomplete
 > functionality with Tab _and_ the buffer is shown.

Could you try doing that?  I have no idea where to start.

martin