Rollup merge of #23607 - mahkoh:cursor, r=alexcrichton

Closes #23599

r? @alexcrichton

diff --combined src/libstd/io/cursor.rs
index 87e5a2a448855f97da265eeeccc38aa1c2ae16fe,e6debeb2a9ce7757fd16f1ff7598c14e5518624e..0dde464267786dcb3dd8a367f7934ad8803b900e
--- 1/src/libstd/io/cursor.rs
--- 2/src/libstd/io/cursor.rs
+++ b/src/libstd/io/cursor.rs
@@@ -31,6 -31,7 +31,7 @@@ use slice
  /// over `T` itself. Instead, specific implementations are provided for various
  /// in-memory buffer types like `Vec<u8>` and `&[u8]`.
  #[stable(feature = "rust1", since = "1.0.0")]
+ #[derive(Clone, Debug)]
  pub struct Cursor<T> {
      inner: T,
      pos: u64,
@@@ -277,7 -278,7 +278,7 @@@ mod tests 
      fn read_to_end() {
          let mut reader = Cursor::new(vec!(0, 1, 2, 3, 4, 5, 6, 7));
          let mut v = Vec::new();
 -        reader.read_to_end(&mut v).ok().unwrap();
 +        reader.read_to_end(&mut v).unwrap();
          assert_eq!(v, [0, 1, 2, 3, 4, 5, 6, 7]);
      }