message: Direct GLUT include in viewer no longer required
diff: #include <string>
  #include <thread>
  -#include <visionaray/detail/platform.h>
  -
  -#if defined(VSNRAY_OS_DARWIN)
  -
  -#include <AvailabilityMacros.h>
  -
  -#if MAC_OS_X_VERSION_MIN_REQUIRED >= MAC_OS_X_VERSION_10_9
  -
  - #pragma GCC diagnostic ignored "-Wdeprecated"
  - #pragma GCC diagnostic ignored "-Wdeprecated-declarations"
  -
  -#endif
  -
  -#include <GLUT/glut.h>
  -
  -#else // VSNRAY_OS_DARWIN
  -
  -#include <GL/glut.h>
  -
  -#endif
  -
  #include <imgui.h>
  #include <Support/CmdLine.h>
  