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This is taken from RosettaCode

This fixes the problem of 3b2d170d and bdc545ff
for good.

In the previous version I had a conjg in there,
but that turned out to be nonsense. To see why,
see the comment in 3b2d170d (spoiler alert: it has
to do with a peculiarity of IEEE 754)

The easiest way to treat complex arguments is to
just normalise them away..

In bdc545ff we have introduced a conjg the
Bernoulli polynomial. It is not clear why.

Courtesy to Roman Zwicky and Ben Pullin for
pointing this out.