Some changes to part 3 of face splitting. Currently held within an if(0) check
When changed to if(1), causes problems for the faces that are visible using
paraview - without part 3, the same faces cause problems but the problems are
less visible. Suspect internal faces (part 4) are causing the issues but
it does not seem to be with either orientation or owner/neighbour designation.

Pushing changes just to keep updated. Some small amout of refactoring into
separate function (myCombineFaces(..)), which is called from both part 3
(currently unused, but probably needed), and part 4.