ENH:Make some methods virtual that some derived class can override.
ENH:Make some methods virtual that some derived class can override.

biddisco/VTK,jmerkow/VTK,keithroe/vtkoptix,berendkleinhaneveld/VTK,cjh1/VTK,mspark93/VTK,berendkleinhaneveld/VTK,johnkit/vtk-dev,demarle/VTK,berendkleinhaneveld/VTK,sumedhasingla/VTK,berendkleinhaneveld/VTK,Wuteyan/VTK,cjh1/VTK,cjh1/VTK,sankhesh/VTK,jeffbaumes/jeffbaumes-vtk,Wuteyan/VTK,biddisco/VTK,naucoin/VTKSlicerWidgets,collects/VTK,SimVascular/VTK,cjh1/VTK,arnaudgelas/VTK,aashish24/VTK-old,spthaolt/VTK,cjh1/VTK,jmerkow/VTK,biddisco/VTK,berendkleinhaneveld/VTK,SimVascular/VTK,spthaolt/VTK,SimVascular/VTK,collects/VTK,sankhesh/VTK,SimVascular/VTK,hendradarwin/VTK,sumedhasingla/VTK,sankhesh/VTK,mspark93/VTK,candy7393/VTK,ashray/VTK-EVM,biddisco/VTK,SimVascular/VTK,candy7393/VTK,keithroe/vtkoptix,naucoin/VTKSlicerWidgets,jmerkow/VTK,SimVascular/VTK,msmolens/VTK,johnkit/vtk-dev,gram526/VTK,gram526/VTK,msmolens/VTK,collects/VTK,candy7393/VTK,candy7393/VTK,ashray/VTK-EVM,spthaolt/VTK,demarle/VTK,SimVascular/VTK,keithroe/vtkoptix,daviddoria/PointGraphsPhase1,daviddoria/PointGraphsPhase1,sankhesh/VTK,jmerkow/VTK,sankhesh/VTK,johnkit/vtk-dev,ashray/VTK-EVM,candy7393/VTK,jeffbaumes/jeffbaumes-vtk,jeffbaumes/jeffbaumes-vtk,jeffbaumes/jeffbaumes-vtk,sankhesh/VTK,arnaudgelas/VTK,SimVascular/VTK,ashray/VTK-EVM,hendradarwin/VTK,sumedhasingla/VTK,hendradarwin/VTK,demarle/VTK,mspark93/VTK,ashray/VTK-EVM,daviddoria/PointGraphsPhase1,Wuteyan/VTK,daviddoria/PointGraphsPhase1,demarle/VTK,jeffbaumes/jeffbaumes-vtk,jmerkow/VTK,jeffbaumes/jeffbaumes-vtk,hendradarwin/VTK,msmolens/VTK,Wuteyan/VTK,gram526/VTK,sankhesh/VTK,berendkleinhaneveld/VTK,keithroe/vtkoptix,aashish24/VTK-old,spthaolt/VTK,ashray/VTK-EVM,demarle/VTK,hendradarwin/VTK,biddisco/VTK,gram526/VTK,arnaudgelas/VTK,msmolens/VTK,arnaudgelas/VTK,aashish24/VTK-old,sankhesh/VTK,hendradarwin/VTK,Wuteyan/VTK,biddisco/VTK,jmerkow/VTK,keithroe/vtkoptix,jmerkow/VTK,johnkit/vtk-dev,ashray/VTK-EVM,sumedhasingla/VTK,msmolens/VTK,gram526/VTK,Wuteyan/VTK,mspark93/VTK,biddisco/VTK,aashish24/VTK-old,jmerkow/VTK,candy7393/VTK,naucoin/VTKSlicerWidgets,msmolens/VTK,spthaolt/VTK,cjh1/VTK,arnaudgelas/VTK,sumedhasingla/VTK,aashish24/VTK-old,johnkit/vtk-dev,johnkit/vtk-dev,mspark93/VTK,Wuteyan/VTK,keithroe/vtkoptix,candy7393/VTK,johnkit/vtk-dev,collects/VTK,candy7393/VTK,daviddoria/PointGraphsPhase1,collects/VTK,spthaolt/VTK,sumedhasingla/VTK,aashish24/VTK-old,mspark93/VTK,demarle/VTK,gram526/VTK,hendradarwin/VTK,gram526/VTK,daviddoria/PointGraphsPhase1,naucoin/VTKSlicerWidgets,ashray/VTK-EVM,msmolens/VTK,arnaudgelas/VTK,demarle/VTK,keithroe/vtkoptix,naucoin/VTKSlicerWidgets,mspark93/VTK,keithroe/vtkoptix,gram526/VTK,berendkleinhaneveld/VTK,sumedhasingla/VTK,collects/VTK,naucoin/VTKSlicerWidgets,spthaolt/VTK,mspark93/VTK,demarle/VTK,sumedhasingla/VTK,msmolens/VTK