Allow unknown features to bootstrap rustc with box_syntax feature.

Specifically added to the test, librustc_trans, librustc_typeck crates.

src/librustc_trans/lib.rs

@@ -22,6 +22,7 @@
       html_favicon_url = "http://www.rust-lang.org/favicon.ico",
       html_root_url = "http://doc.rust-lang.org/nightly/")]
 
+#![allow(unknown_features)]
 #![feature(quote)]
 #![feature(slicing_syntax, unsafe_destructor)]
 #![feature(box_syntax)]

src/librustc_typeck/lib.rs

@@ -71,6 +71,7 @@ This API is completely unstable and subject to change.
       html_favicon_url = "http://www.rust-lang.org/favicon.ico",
       html_root_url = "http://doc.rust-lang.org/nightly/")]
 
+#![allow(unknown_features)]
 #![feature(quote)]
 #![feature(slicing_syntax, unsafe_destructor)]
 #![feature(box_syntax)]

src/libtest/lib.rs

@@ -30,6 +30,7 @@
 #![doc(html_logo_url = "http://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
        html_favicon_url = "http://www.rust-lang.org/favicon.ico",
        html_root_url = "http://doc.rust-lang.org/nightly/")]
+#![allow(unknown_features)]
 #![feature(asm, slicing_syntax)]
 #![feature(box_syntax)]