ENH: Pass strings to comparison function by reference.
ENH: Pass strings to comparison function by reference.

This yields a 20x speedup when sorting a list of ~5000 filenames (VS 2008).

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