The following little function appears to trigger a bug
in integer math.
It returns -11 rather than -10 as expected. The
problem seems to be in pint_neg; commenting all of
that function out except the fallback
psco_generic_call makes things work fine, while doing
the same to pint_abs does not. I would suspect
integer_negative, but I don't understand that part of
Psyco enough to attempt to debug it.