message: Use eprintln! instead of println!.
  This prevents debug output from being sent to stdout.
diff: @@ -222,7 +222,7 @@ impl Context {
  {
  let mut ctxt = context.make_current();
  if crate::get_gl_error(&mut ctxt).is_some() {
  - println!("glium has triggered an OpenGL error during initialization. Please report \
  + eprintln!("glium has triggered an OpenGL error during initialization. Please report \
  this error: https://github.com/glium/glium/issues");
  }
  /*assert!(::get_gl_error(&mut ctxt).is_none(),
  @@ -840,7 +840,7 @@ fn default_debug_callback(_: debug::Source, ty: debug::MessageType, severity: de
  };
  if report_debug_output_errors {
  - print!("Debug message with high or medium severity: `{}`.\n\
  + eprint!("Debug message with high or medium severity: `{}`.\n\
  Please report this error: https://github.com/glium/glium/issues\n\
  Backtrace:",
  message);
  @@ -867,7 +867,7 @@ fn default_debug_callback(_: debug::Source, ty: debug::MessageType, severity: de
  true
  });
  - println!("\n");
  + eprintln!("\n");
  }
  }
  @@ -875,7 +875,7 @@ fn default_debug_callback(_: debug::Source, ty: debug::MessageType, severity: de
  fn printall_debug_callback(source: debug::Source, ty: debug::MessageType, severity: debug::Severity,
  id: u32, _: bool, message: &str)
  {
  - println!("Source: {src:?}\t\tSeverity: {sev:?}\t\tType: {ty:?}\t\tId: {id}\n{msg}",
  + eprintln!("Source: {src:?}\t\tSeverity: {sev:?}\t\tType: {ty:?}\t\tId: {id}\n{msg}",
  src = source, sev = severity, ty = ty, id = id, msg = message);
  }
  