Rollup merge of #22952 - huonw:missing-stable, r=alexcrichton

 Unstable is the conservative choice.

cc #22950.

diff --combined src/libcore/iter.rs
index 518ec05f5b980944e5c06b5116b1835bd1c3c0dc,57a6613debd583d4d3cbaf550548f84f02809c55..13d219ec674bce849ed942cd4f1e14a9ca814098
--- 1/src/libcore/iter.rs
--- 2/src/libcore/iter.rs
+++ b/src/libcore/iter.rs
@@@ -2061,6 -2061,7 +2061,7 @@@ pub struct Scan<I, St, F> 
      f: F,
  
      /// The current internal state to be passed to the closure next.
+     #[unstable(feature = "core")]
      pub state: St,
  }
  
@@@ -2338,6 -2339,7 +2339,7 @@@ impl<I: RandomAccessIterator, F> Random
  pub struct Unfold<St, F> {
      f: F,
      /// Internal state that will be passed to the closure on the next iteration
+     #[unstable(feature = "core")]
      pub state: St,
  }
  
@@@ -2467,7 -2469,7 +2469,7 @@@ impl<A: Int + ToPrimitive> Iterator fo
              Some(a) => {
                  let sz = self.stop.to_i64().map(|b| b.checked_sub(a));
                  match sz {
 -                    Some(Some(bound)) => bound.to_uint(),
 +                    Some(Some(bound)) => bound.to_usize(),
                      _ => None,
                  }
              },
@@@ -2475,7 -2477,7 +2477,7 @@@
                  Some(a) => {
                      let sz = self.stop.to_u64().map(|b| b.checked_sub(a));
                      match sz {
 -                        Some(Some(bound)) => bound.to_uint(),
 +                        Some(Some(bound)) => bound.to_usize(),
                          _ => None
                      }
                  },
@@@ -2741,7 -2743,7 +2743,7 @@@ impl<A: Int> Iterator for ::ops::Range<
          if self.start >= self.end {
              (0, Some(0))
          } else {
 -            let length = (self.end - self.start).to_uint();
 +            let length = (self.end - self.start).to_usize();
              (length.unwrap_or(0), length)
          }
      }