rollup merge of #22459: alexcrichton/feature-names

Conflicts:
	src/rustbook/main.rs

src/libserialize/lib.rs

@@ -29,8 +29,8 @@ Core encoding and decoding interfaces.
 #![feature(collections)]
 #![feature(core)]
 #![feature(int_uint)]
-#![feature(io)]
-#![feature(path)]
+#![feature(old_io)]
+#![feature(old_path)]
 #![feature(hash)]
 #![feature(rustc_private)]
 #![feature(staged_api)]