If the option is on, then vertical layout has code on top, output on bottom,
and horizontal has code on left, output on right.

Also, with code on top, changed notebook tabs to be on top too.

When panes are swapped (edit on top), the autocomplete popup now stretches DOWN from the cursor, not up.  This makes it so it won't extend up off the screen.

Previous fix caused the autocomplete box to overlap the cursor.  We adjust its position by lineheight to avoid this.

The problem seems to be due to the _n_unclaimed_results counter somehow getting out of sync.
At some point, this counter is incremeneted but not properly decremented.
The result is that DreamPie keeps saying "subprocess is busy", thinking it is waiting for a result, but there really isn't any result coming, so it waits forever.
(This waiting occurs in DreamPie.call_subp_noblock, which is called from execute_source.)

The "solution" is to add a simple method to the DreamPie class that just decrements _n_unclaimed_results.
I then added a menu item to call this function.
If this "stuck" situation arises, you can clear it by using this manual override.
Note that using this when the subprocess is *not* stuck could cause havoc, so be careful!