SF [2159499] Full bigfloat precision for Gamma after the second call



van Nek wrote:
> Richard suggested iroot. I think, here I will make some tests concerning speed. 
> I am using gcl on Windows and I can also check it with clisp on ubuntu. 
> I'll let you know. (But not today.)

Sounds good.  If you're going to do some speed tests, I think it would
be good to try some with fpprec just over 36*2^n.  This is the case
where, after n iterations, we're just below the desired precision, and
we need another iteration, effectively doubling the number of bits in
the computation.

Ray