Twinax cable over ground plane test case.

Two models are genereated here, the first using FastHenry and the second
using the original SACAMOS model with L and C matrices calculated using the
Laplace solver.

FD_TWINAX2_OVER_GROUND_FASTHENRY

FD_TWINAX2_OVER_GROUND_LAPLACE

A comparison of the results of the models can be plotted with the command

gnuplot plot_comparison.plt

Note that we have no external validation for this test case and we cannot
use the SACAMOS internal validation process with the zc_validation flag as
this is a multi-domain problem. It is felt that the results from the
FastHenry model are not accurate due to issues with rational function fitting.