Update vtkpng from libpng-1.0.12 to libpng-1.0.63.
All versions of libpng prior to 1.0.16 had severe security flaws.
Renamed pngDllConfig.h to vtkpngConfig.h to make it clear that this header is for VTK.
All versions of libpng prior to 1.0.16 had severe security flaws.
Renamed pngDllConfig.h to vtkpngConfig.h to make it clear that this header is for VTK.