consistency update for null pointers

- uniform use of reinterpret_cast<foo*>(0) instead of
  reinterpret_cast<foo*>(NULL)

- make all static null() members inline since they are really only a cast:
      "*reinterpret_cast<foo*>(0)"

applications/utilities/mesh/conversion/fluentMeshToFoam/create3DCellShape.C

@@ -51,7 +51,7 @@ cellShape create3DCellShape
     static List<const cellModel*> fluentCellModelLookup
     (
         7,
-        reinterpret_cast<const cellModel*>(NULL)
+        reinterpret_cast<const cellModel*>(0)
     );
 
     fluentCellModelLookup[2] = cellModeller::lookup("tet");