API: Deprecate .fold_while() in favour of .try_fold()

Author: bluss

src/lib.rs

@@ -1767,6 +1767,7 @@ pub trait Itertools : Iterator {
     /// The big difference between the computations of `result2` and `result3` is that while
     /// `fold()` called the provided closure for every item of the callee iterator,
     /// `fold_while()` actually stopped iterating as soon as it encountered `Fold::Done(_)`.
+    #[deprecated(note="Use .try_fold() instead", since="0.8")]
     fn fold_while<B, F>(&mut self, init: B, mut f: F) -> FoldWhile<B>
         where Self: Sized,
               F: FnMut(B, Self::Item) -> FoldWhile<B>

tests/test_std.rs

@@ -702,6 +702,7 @@ fn while_some() {
     it::assert_equal(ns, vec![1, 2, 3, 4]);
 }
 
+#[allow(deprecated)]
 #[test]
 fn fold_while() {
     let mut iterations = 0;