message: Really compile w/o pbrtParser present (?)
diff: #include "model.h"
  #include "sg.h"
  -using namespace pbrt;
  -
  namespace visionaray
  {
  #if VSNRAY_COMMON_HAVE_PBRTPARSER
  +using namespace pbrt;
  +
  mat4 make_mat4(affine3f const& aff)
  {
  mat4 result = mat4::identity();
  