[Spot] Behavior change in autfilt from 2.9.7 to 2.10

Hi,

When invoking `autfilt sub.aut --included-in=sup.aut` on the two enclosed Buchi automata with Spot 2.10 I am getting:

``` Too many acceptance sets used. The limit is 32. ```

With Spot 2.9.7 I was getting a non-terminating execution.

Is it the expected result? If so, what is the explanation behind the too many acceptance sets? Is it the complementation procedure for `sup.aut` that fails?

Thank you and keep up with the excellent work, Pierre.