added 'require Tk' for windows users
added 'require Tk' for windows users

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