Do not scroll sclices with mouse modifiers depressed
Do not scroll sclices with mouse modifiers depressed

The slice scroll in the previous commit should work only when
there are no mouse modifiers depressed

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