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- fixed indexing error (crashes under windows).
  No crash but still incorrect on other systems

- makes the intent clearer and avoids the need for additional
  constructor casting. Eg,

      labelList(10, Zero)    vs.  labelList(10, 0)
      scalarField(10, Zero)  vs.  scalarField(10, scalar(0))
      vectorField(10, Zero)  vs.  vectorField(10, vector::zero)

- nBoundaryFaces() is often used and is identical to
  (nFaces() - nInternalFaces()).

- forward the mesh nInternalFaces() and nBoundaryFaces() to
  polyBoundaryMesh as nFaces() and start() respectively,
  for use when operating on a polyBoundaryMesh.

STYLE:

- use identity() function with starting offset when creating boundary maps.

     labelList map
     (
         identity(mesh.nBoundaryFaces(), mesh.nInternalFaces())
     );

  vs.

     labelList map(mesh.nBoundaryFaces());
     forAll(map, i)
     {
         map[i] = mesh.nInternalFaces() + i;
     }

- in 2.4.x the general default for polyMesh::findCell was FACE_DIAG_TRIS,
  but this was changed to CELL_TETS for better handling of concave
  cells.

- in snappyHexMesh meshRefinement, findCell is used to define
  locations in mesh and cells for closer refinement. Using CELL_TETS
  causes an octree rebuild when the mesh has changed and this adds
  considerable overhead. For this operation, the faster FACE_DIAG_TRIS
  mode can be used instead.

- this represents a partial revert for commit 6a0a8b99

ENH: add degToRad() multiplier (useful for scalar fields)

- use degToRad() functions throughout instead of scattered local solutions

It was ignoring the initial selection of cells inside/outside the refinement
region and instead looking at all surface-intersection regardless. Fixes #51.

- shoot rays to nearest point on surface and two perpendicular rays
  (instead of always shooting in the 3 coordinate directions)

- avoid bleeding through the surface intersection

1. multi-ray shooting. It now shoots rays in all the 3 coordinate directions
from the cell centre. Before it would shoot just a single ray from the
nearest point on the surface, going through the cell centre.

There is a cost overhead in that now it shoots 6 rays (+-x, +-y, +-z)
instead of just 1.

2. bleeding of refinement. It marks the cells inside a gap and walks out
the gap-size to neighbouring cells (which are just outside the gap). This
should make for a smoother refinement pattern.