ENH: Pre-allocate space for the vtkImageStencilData extents.
ENH: Pre-allocate space for the vtkImageStencilData extents.

Since calls to new/delete are expensive, it makes sense to pre-allocate
a block of memory with enough space for one stencil extent per row.
Without this pre-allocation, creating a stencil would usually require
one "new" per row.

Change-Id: I8aca67e8d20753e06d17bb89dc85bf8950e2f388

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