speed of unbalanced division

[Zimmermann Paul]

       Hi Torbjörn,

> I got back to this now, and finally committed a patch.
> 
> New diagrams at gmplib.org/devel/.
> 
> Things are still not perfect.  More work is needed.

thank you for the feedback. Yes the new curve is not everywhere optimal, but
the important thing is that it is much more regular, which is critical
for algorithms assuming that when we cut both numerator and divisor (for
a fixed-size quotient) the time will decrease (or at least not increase).

Paul