rustc: "tag" -> "enum"

src/comp/syntax/ext/base.rs

@@ -11,7 +11,7 @@ type macro_def = {ident: str, ext: syntax_extension};
 type macro_definer =
     fn@(ext_ctxt, span, @ast::expr, option::t<str>) -> macro_def;
 
-tag syntax_extension {
+enum syntax_extension {
     normal(syntax_expander);
     macro_defining(macro_definer);
 }