to Mattijs' work are:

+ Correct use of normals and cosine (dot product) to identify planar
  faces.

+ Correct use for lambda in tracking - it is a fraction, not a distance.

+ Not doing a reduce on demand driven construction data - not all
  processors call it at the same time, so crashes.

This implementation contains an attempt at making the calculation of
lambdaC (from the cell centre) use decomposed triangles for faces, but
this is a bad approach, the concept of using lambdaC relies on the
definition of a convex polyhedron, i.e. none of the planes of the
faces of the polyhedron are inside the volume.  Can't use this method
and will need to treat a convex cell completely differently, not just
some of its faces.

list build PPFE.

floating point error and is pointless.

WallSpringSliderDashpot model.

Correctly identifying non-flat - sharp - wall interactions, i.e. with
concave points and edges.  Rigoruous methods for exclusion distances
of existing wall interaction sites.

Separated off wall force calculation into WallSpringSliderDashpot
model.

functions.

only so far.  Wall force model hard-coded.

so move everything to a vectorField or a pointField.  Changed accessor
for a ReferredCells points to points().

Renamed PairFunction to PairModel, so will fit in with WallModel,
rather than WallFunction, a confusion waiting to happen.

of the referred cells.  To be used by wall interactions.

the InteractingKinematicParcel, using in the SpringSliderDashpot
model.  Correctly determining extreme properties for the timestep
subCycling calculation.

than when it is initialised.  This allows messages to be created and added to.

wall patch faces that each cell is potentially in range of.

which faces are from wall patches.

Moving ReferredCell into a subdirectory of ReferredCellList.

determines the number of subcycles needed to satisfy its timestep
requirements.