message: disable KHR_debug messages
  there were never useful and in fact harmful, because confusing to our
  users.
diff: @@ -268,7 +268,9 @@ OpenGLContext::OpenGLContext() noexcept {
  }
  #endif
  -#if !defined(NDEBUG) && defined(GL_KHR_debug)
  + // in practice KHR_Debug has never been useful, and actually is confusing. We keep this
  + // only for our own debugging, in case we need it some day.
  +#if false && !defined(NDEBUG) && defined(GL_KHR_debug)
  if (ext.KHR_debug) {
  auto cb = +[](GLenum, GLenum type, GLuint, GLenum severity, GLsizei length,
  const GLchar* message, const void *) {
  