message: fix cascade file discovery
diff: @@ -12,17 +12,26 @@ use opencv::{
  fn run() -> opencv::Result<()> {
  let window = "video capture";
  - let xml = "/usr/local/share/OpenCV/haarcascades/haarcascade_frontalface_alt.xml";
  highgui::named_window(window, 1)?;
  #[cfg(feature = "opencv-32")]
  - let mut cam = videoio::VideoCapture::new(0)?; // 0 is the default camera
  + let (xml, mut cam) = {
  + (
  + "/usr/share/OpenCV/haarcascades/haarcascade_frontalface_alt.xml".to_owned(),
  + videoio::VideoCapture::new(0)?, // 0 is the default camera
  + )
  + };
  #[cfg(not(feature = "opencv-32"))]
  - let mut cam = videoio::VideoCapture::new_with_backend(0, videoio::CAP_ANY)?; // 0 is the default camera
  + let (xml, mut cam) = {
  + (
  + core::find_file("haarcascades/haarcascade_frontalface_alt.xml", true, false)?,
  + videoio::VideoCapture::new_with_backend(0, videoio::CAP_ANY)?, // 0 is the default camera
  + )
  + };
  let opened = videoio::VideoCapture::is_opened(&cam)?;
  if !opened {
  panic!("Unable to open default camera!");
  }
  - let mut face = objdetect::CascadeClassifier::new(xml)?;
  + let mut face = objdetect::CascadeClassifier::new(&xml)?;
  loop {
  let mut frame = Mat::new()?;
  cam.read(&mut frame)?;
  