COMP: Update VTK to fix build error on Debian "Jessie". Fixes 0003906

Co-authored-by: "Sharp, Gregory C." <GCSHARP@mgh.harvard.edu>

This commit fixes the following build error:

// ----------------
[ 35%] Building CXX object Rendering/OpenGL/CMakeFiles/vtkRenderingOpenGLObjects.dir/vtkXOpenGLRenderWindow.cxx.o
In file included from /usr/include/GL/glx.h:333:0,
from /home/gsharp/build/slicer-4/Slicer-build/VTKv6/Rendering/OpenGL/vtkXOpenGLRenderWindow.cxx:30:
/usr/include/GL/glxext.h:480:143: error: ‘GLintptr’ has not been declared
typedef void ( PFNGLXCOPYBUFFERSUBDATANVPROC) (Display dpy, GLXContext readCtx, GLXContext writeCtx, GLenum readTarget, GLenum writeTarget, GLintptr readOffset, GLintptr writeOffset, GLsizeiptr size);
// ----------------

$ git shortlog ea7cdc4..563cc62 --no-merges
Marcus D. Hanwell (1):
Actually define GLX_GLXEXT_LEGACY to prevent the include

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23861 3bd1e089-480b-0410-8dfb-8563597acbee