auto merge of #7706 : sanxiyn/rust/qualification-lint, r=pcwalton

Fix #2551.

Lint is off by default because I didn't bother to fix all of std and extra.

src/libsyntax/ast_util.rs

@@ -462,6 +462,7 @@ pub fn id_visitor<T: Copy>(vfn: @fn(node_id, T)) -> visit::vt<T> {
         },
 
         visit_ty: |ty, (t, vt)| {
+            vfn(ty.id, copy t);
             match ty.node {
               ty_path(_, _, id) => vfn(id, copy t),
               _ => { /* fall through */ }