Program creates a new trace with the larger number of points.
Note that the calling program is then responsible for transferring the file header information into the new trace. This uses a modified 'spline-like' slope matching algorithm. A different cubic polynomial is derived for each 4 point region. Y1 and Y2 are the Y values of these two end point points. Also, Y0 and Y3 are the Y values of the points just before and after the former.