ENH: fix configure error if MPI_EXTRA_LIBRARY is not set.
ENH: fix configure error if MPI_EXTRA_LIBRARY is not set.

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