Add #![feature] attributes to doctests

src/libstd/lib.rs

@@ -105,6 +105,7 @@
        html_favicon_url = "http://www.rust-lang.org/favicon.ico",
        html_root_url = "http://doc.rust-lang.org/nightly/",
        html_playground_url = "http://play.rust-lang.org/")]
+#![doc(test(no_crate_inject))]
 
 #![feature(alloc)]
 #![feature(box_syntax)]