librustc: Make unqualified identifier searches terminate at the nearest module scope. r=tjc

src/libsyntax/ast_util.rs

@@ -8,10 +8,13 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+use core::prelude::*;
+
 use ast::*;
 use ast;
 use ast_util;
 use codemap::{span, BytePos};
+use parse::token;
 use visit;
 
 use core::cmp;