need 2-point halo all the way around
need 2-point halo all the way around

LocalRange includes vertices of cell CellLocalRange.Begin()-1, so overlap detection
will generate overlap data for this cell. if generating cubic isoparametric coordinates,
need data from CellLocalRange.Begin()-2, hence 2 points/cells in halo

majosm/overkit,majosm/overkit,majosm/overkit,majosm/overkit