alloc: Forward ExactSizeIterator methods in Iterator for Box<I>

src/liballoc/lib.rs

@@ -79,6 +79,7 @@
 #![feature(core_intrinsics)]
 #![feature(custom_attribute)]
 #![feature(dropck_parametricity)]
+#![cfg_attr(not(test), feature(exact_size_is_empty))]
 #![feature(fundamental)]
 #![feature(lang_items)]
 #![feature(needs_allocator)]