ENH: improvements for isoSurfaceTopo erosion (#1374)

- adapted openfoam.org code.  Original commit message:

  Instead of adapting tet base points cell-by-cell, the dangling
  points are pre-computed and then the adaptations to the base points
  are made face-by-face. This correctly adapts faces which have
  different dangling points relative to the owner and neighbour cells.