- takes a direct approach of determining which cells are cut and walks
the cell faces directly to build the resulting surface.
- better handling of corner cases.
* Avoids redundant points when the cut passes exactly through a
mesh point.
* Supresses generation of duplicates faces when the plane cut
coincides exactly with a mesh face.
- for severely concave cells where the plane cuts a face multiple times
there is currently no remedial action taken, except to note the
failure and unwind the insertion of the corresponding points and
faces.
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