Cautionary extra naturals

[Rune Zedeler]

When I left hacking the accidental engraver some 4 years ago, we were
talking about how to implement cautionary extra naturals - that is, so
that modern cautionaries would yield

| # O    |  (n)b O  |

(where O is a whole note and n is a natural)

Until we came up with a solution for how best to implement that, the
accidental engraver was temporarily left outputting the above as

| # O    |  (nb) O  |

because the correct output was not possible.
I see that the problem still persists.

What should we do?

I really think that (n)b should be possible, because none of the other
solutions yield consistant results.

-Rune