Fix warnings in script_traits.

components/script_traits/lib.rs

@@ -2,10 +2,12 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+#![feature(core)]
 #![feature(int_uint)]
+#![feature(libc)]
+#![feature(rustc_private)]
 
 #![allow(missing_copy_implementations)]
-#![allow(unstable)]
 
 extern crate devtools_traits;
 extern crate geom;