Alternative bernoulli(const numeric &)

[Markus Nullmeier]

Maybe bernoulli() should warn if some user tries to feed it
an even number greater than 23168, since that would give an
integer >= 2^29, wrongly converted to cln::cl_I in the line
with "exquo".

On the other hand, I don't know how much time and memory
would be wasted before that happens. Already bernoulli(5000)
takes 10 minutes and 10 megs on an Athlon 900.

Markus