ENH: Faster lookup index clamping.
ENH: Faster lookup index clamping.

This is a small change to improve performance, it causes
the clamping code to compile into minsd/maxsd instructions
instead of branching (tested on gcc 4.2 x86 with sse2).

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