Plotting wiggle traces in true offset with SUXWIGB

It is possible to plot wiggle traces in true offset, that is to say, to take the values for the horizontal dimension of the wiggle plot from the values in the header. This is done with the ``key='' parameter.

For example, lets make some test data with suplane and plot it using the ``key=offset'' via:

% suplane | suchw key1=offset key2=tracl a=0 b=100  | suxwigb key=offset   &

The result is a plot with the x2 axis labeled in the values of the offset header field (which count by 100's).