Change "file" of injected string from "-" to "<anon>", less confusing

that way.

Author: kevina

src/comp/syntax/ext/expand.rs

@@ -70,7 +70,7 @@ fn expand_crate(sess: session::session, c: @crate) -> @crate {
         {fold_expr: bind expand_expr(exts, cx, _, _, afp.fold_expr)
             with *afp};
     let f = make_fold(f_pre);
-    let cm = parse_expr_from_source_str("-", core_macros(),
+    let cm = parse_expr_from_source_str("<anon>", core_macros(),
                                         sess.opts.cfg,
                                         sess.parse_sess);