Small chaange with reading VTU files so that char and string methods are congruent.

include/FEM4EllipticPDE.h

             /**
              *  Read grid in from VTK file
              */
-            void SetVTUGridFile( std::string& vtkGridFile );
+            void SetVTUGridFile( const std::string& vtkGridFile );
 
             /**
              *  Read grid in from VTK file
              */
-            void SetVTUGridFile( char* vtkGridFile );
+            void SetVTUGridFile( const char* vtkGridFile );
 
             /** Sets up a DC problem with a survey
              *  @param[in] ij is the injection index

src/FEM4EllipticPDE.cpp

     //       Class:  FEM4EllipticPDE
     //      Method:  SetVTUGridFile
     //--------------------------------------------------------------------------------------
-    void FEM4EllipticPDE::SetVTUGridFile ( std::string& fname  ) {
-        std::cout  << "Loading VTK .vtu file " << fname;
-        vtkXMLUnstructuredGridReader* MeshReader = vtkXMLUnstructuredGridReader::New();
-        MeshReader->SetFileName(fname.c_str());
-        MeshReader->Update();
-        //vtkGrid->DeepCopy( MeshReader->GetOutput() );
-        //vtkGrid->ShallowCopy( MeshReader->GetOutput() );
-        vtkGrid = MeshReader->GetOutput();
-        MeshReader->Delete();
-        std::cout  << " Finished! " << std::endl;
+    void FEM4EllipticPDE::SetVTUGridFile ( const std::string& fname  ) {
+        SetVTUGridFile( fname.c_str() );
         return ;
     }		// -----  end of method FEM4EllipticPDE::SetVTKGridFile  -----
 
     //       Class:  FEM4EllipticPDE
     //      Method:  SetVTUGridFile
     //--------------------------------------------------------------------------------------
-    void FEM4EllipticPDE::SetVTUGridFile ( char* fname  ) {
+    void FEM4EllipticPDE::SetVTUGridFile ( const char* fname  ) {
         std::cout  << "Loading VTK .vtu file " << fname;
         vtkXMLUnstructuredGridReader* MeshReader = vtkXMLUnstructuredGridReader::New();
         MeshReader->SetFileName(fname);