Rev::rposition counts from the wrong end

Because of a compiler bug that adding `Self: ExactSizeIterator` makes
the compiler forget `Self::Item` is `<I as Iterator>::Item`, we remove
this specialization for now.

Author: sfanxiang

src/libcore/iter/adapters/mod.rs

@@ -66,13 +66,6 @@ impl<I> Iterator for Rev<I> where I: DoubleEndedIterator {
     {
         self.iter.rfind(predicate)
     }
-
-    #[inline]
-    fn rposition<P>(&mut self, predicate: P) -> Option<usize> where
-        P: FnMut(Self::Item) -> bool
-    {
-        self.iter.position(predicate)
-    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]

src/libcore/tests/iter.rs

@@ -1688,6 +1688,12 @@ fn test_rposition() {
     assert!(v.iter().rposition(g).is_none());
 }
 
+#[test]
+fn test_rev_rposition() {
+    let v = [0, 0, 1, 1];
+    assert_eq!(v.iter().rev().rposition(|&x| x == 1), Some(1));
+}
+
 #[test]
 #[should_panic]
 fn test_rposition_panic() {