and prevent a divide by zero

Conflicts:
	applications/test/Matrix/Test-Matrix.C
	applications/utilities/mesh/generation/extrude2DMesh/extrude2DMesh/extrude2DMesh/extrude2DMesh.C
	applications/utilities/mesh/generation/extrude2DMesh/extrude2DMesh/extrude2DMesh/extrude2DMesh.H
	src/OpenFOAM/algorithms/indexedOctree/indexedOctree.C
	src/OpenFOAM/primitives/Tensor2D/Tensor2DI.H

+ Move most of the octree searching functionality from triSurfaceMesh into
  triSurfaceSearch. Much of it was duplicated anyway.
+ Add triSurfaceRegionSearch, which constructs an octree for each region in
  a surface and performs searches on specified regions only.