ENH: VTK_USE_SYSTEM_FREETYPE was not really working. VTK would never use the System freetype library when indicated. Fixed that. The vtk-provided vtkfreetype is mangled. Consequently one must include "vtk_freetype.h" instead of <ft2build.h> to ensure that the correct ft2build.h file gets included (changed the ftgl/src files to fix this). vtkFreeTypeUtilities compiles in the caching code only when FreeType version is  >= 2.1.9. This should overcome compilation issues when using older system FreeType. Ofcourse, we will get runtime error if on uses functions that rely on the cache subsystem on such builds.