foamToVTK, PVFoamReader: Resolve problems converting VTK_WEDGE

- There will be triangles rendered inside the mesh (when
    surface-rendering), because one of the cell's triangles is defined
    as a quadrangle in VTK_WEDGE.

  - Therefore, this VTK_WEDGE representation is only used when
    decomposing the mesh, otherwise the correct representation is done
    by VTK_POLYHEDRON.

  - Furthermore, using VTK_PYRAMID gave worse result, because it renders
    2 triangles inside the mesh for the collapsed quadrangle, likely due
    to mismatch with the adjacent cell's face.

  - Using VTK_HEXAHEDRON was not tested in this iteration, given that it
    should give even worse results, when compared to using VTK_PYRAMID.

Patch contributed by Bruno Santos
Resolves bug-report http://bugs.openfoam.org/view.php?id=2099

applications/utilities/postProcessing/dataConversion/foamToVTK/foamToVTK/vtkTopo.C

@@ -152,7 +152,7 @@ Foam::vtkTopo::vtkTopo(const polyMesh& mesh)
 
             cellTypes_[celli] = VTK_WEDGE;
         }
-        else if (cellModel == tetWedge)
+        else if (cellModel == tetWedge && decomposePoly)
         {
             // Treat as squeezed prism (VTK_WEDGE)
             vtkVerts.setSize(6);