COMP: Include "vtk_glew.h" instead of "GL/glew.h"

The former properly selects between the VTK-provided and system glew
header.

Change-Id: If39ed4762ce2c4d0ba80248083e8a8e8371fd5c4
Merge topic 'opengl2-include-vtk_glew' into master

c2db066e COMP: Include "vtk_glew.h" instead of "GL/glew.h"