message: add environment variable equivalent to --osp:logoutput
diff: @@ -68,6 +68,15 @@ namespace ospray {
  numThreads = OSPRAY_THREADS.first ? OSPRAY_THREADS.second :
  getParam1i("numThreads", -1);
  + auto OSPRAY_LOG_OUTPUT = getEnvVar<std::string>("OSPRAY_LOG_OUTPUT");
  + if (OSPRAY_LOG_OUTPUT.first) {
  + auto &dst = OSPRAY_LOG_OUTPUT.second;
  + if (dst == "cout")
  + error_fcn = [](const char *msg){ std::cout << msg; };
  + else if (dst == "cerr")
  + error_fcn = [](const char *msg){ std::cerr << msg; };
  + }
  +
  if (debugMode) {
  logLevel = 2;
  numThreads = 1;
  