New branch for editing, allowing return to the master branch if I mess up :)
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.
Changes to hexRef.C, now my mesh constructs without twists in a wider
arrangement of cells / interface.
Added a sortFaces class for diagnostics - this can be removed for a release
library version, but is included here since hexRef4 now depends on the class.
Added an "extended_debug" bool, which is static and accessible from solvers
using hexRef4::extended_debug = 0, 1, true, false, etc.
Some additional changes to comments to try and make slightly clearer in parts.
Will now test the damBreak case sent to me earlier this week and try work out
why that is breaking.

TODO - Part 3 of the face splitting only allows paired faces at present. This
is causing an error for me in my 51st time step for my test case, where
non-paired faces are somehow reaching part 3. Need to see if this is because
they're being missed, and should be handled earlier, or if I must relax the
restrictions on part 3 faces.