Port SourceTarball.bash to run on OS X
Port SourceTarball.bash to run on OS X

Create a compute_MD5 function to abstract the differences between
the Linux "md5sum" tool and the OS X "md5" tool.

Change-Id: I79fdb8347f99a17643a73179bb98dc8c671442b9

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