Fixing vtkPyramid gradient calculation at apex.
Fixing vtkPyramid gradient calculation at apex.

I'm using extrapolation to figure out the proper gradient at the
apex of the pyramid.  I also fixed EvaluatePosition() to work
if the input point is the apex.

Change-Id: I21daea886a442625bf4ea7bdc1e5398529022b3c

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