rollup merge of #22459: alexcrichton/feature-names

Conflicts:
	src/rustbook/main.rs

src/librustc_driver/lib.rs

@@ -28,10 +28,10 @@
 #![feature(core)]
 #![feature(env)]
 #![feature(int_uint)]
-#![feature(io)]
+#![feature(old_io)]
 #![feature(libc)]
 #![feature(os)]
-#![feature(path)]
+#![feature(old_path)]
 #![feature(quote)]
 #![feature(rustc_diagnostic_macros)]
 #![feature(rustc_private)]