To run gnuplot xycontour tests.
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The gnuplot command in ngspice is:

    gnuplot <file> xycontour <expr>

xycontour is a new flag. Only a single <expr> is allowed to be plotted
in a contour diagram. With <expr1> vs <expr2> only <expr1> is plotted.

    ngspice passq.cir

This plots xy contour diagrams for 2d Cider save file data.
On visualc Windows in a cmd shell, run 'winq.cir'.

    ngspice passq1.cir

This checks that gnuplot <file> xycontour <expr> works with 1d data.
The xycontour flag is just ignored.
On visualc Windows in a cmd shell, run 'winq1.cir'.