** When a minibuffer window is active but not the selected window, if<BR>
you try to use the minibuffer, you used to get a nested minibuffer.
Now, this not only gives an error, it also cancels the minibuffer that
was already active.
<P>
The motive for this change is so that beginning users do not
unknowingly move away from minibuffers, leaving them active, and then
get confused by it.
<P>
If you want to be able to have recursive minibuffers, you must
set enable-recursive-minibuffers to non-nil.
<P>