bug#8911: bs-cycle-next deletes window in some cases.

[martin rudalics]

> If the window is dedicated, and the user invokes bs-cycle-next
> (usually, by having it bound to a key, and not realizing that the
> window is dedicated), that's user error, but the user should not be
> penalized; staying is better. Perhaps a message could be shown. Also,
> no new window should be created. For example, I find the current
> behavior
>
>   emacs -Q -l bs
>   C-h N
>   C-h C-c
>   M-: (set-window-dedicated-p (selected-window) t) <RET>
>   M-x bs-cycle-next <RET>
>
> of splitting the window extremely unuseful and unhelpful.

Because it does (switch-to-buffer next) in `bs-cycle-next'?  Well, what
else should it do?  Undedicate the window?  That is a tricky case.

martin