ENH: use double for VTK legacy output (issue #891)

- some paraview versions (eg, on windows) don't support float, only double.

  This mostly affected the vtkSurfaceWriter.

  The foamToVTK is also affected, but since it also supports the XML
  output formats (vtp, vtu) these can be used instead.

tutorials/compressible/rhoSimpleFoam/squareBend/system/samplingDebug

@@ -15,6 +15,7 @@ debug
     sampleScheme  cellPoint;
     interpolationScheme cellPoint;
     surfaceFormat ensight;
+    // surfaceFormat vtk;
 
     formatOptions
     {