Require the parameter that will be referenced to be noted

Issue #918

src/comp/syntax/ast_util.rs

@@ -215,7 +215,7 @@ fn ternary_to_if(e: @expr) -> @expr {
 
 fn ret_by_ref(style: ret_style) -> bool {
     alt style {
-      return_ref(_) { true }
+      return_ref(_, _) { true }
       _ { false }
     }
 }