There's a few plots that have:

  static bool glew_init = false;
  ...
  if(!glew_init) { glewInit(); glew_init = true; }

duplicated.  This centralizes the code, ensuring we only do GLEW
initialization once per process, even if two plots use GLEW.
Further, GLEW init has become more complicated and this prevents
anyone else from having to learn the details.

git-svn-id: http://visit.ilight.com/svn/visit/trunk/src@8017 18c085ea-50e0-402c-830e-de6fd14e8384