Add feature old_io to silence warnings
diff --git a/src/lib.rs b/src/lib.rs
index cb7052e..1e4ec7b 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -45,7 +45,7 @@
 #![deny(missing_docs)]
 
 #![allow(unused_features)] // for `rand` while testing
-#![feature(core, io, test)]
+#![feature(core, io, test, old_io)]
 
 use std::old_io::IoResult;
 use std::mem::transmute;