Lots of changes to make VTK work with both 2.1 and 3.2 versions
of OpenGL. The main differences in OpenGL 3.2 are that the
following features no longer are supported

intensity textures - recoded to use red
luminanace textures - recoded to use red
line stipple - vtk error macro
querying extensions in one string - replaced with multiple calls
pixel transfer bias and scale - recoded to be done in the shader
glPush and PopAttrib - recoded to get and set instead
texelFetchBuffer - defined to texelFetch
txture1D - defined to texture
texture3D - defined to texture