make mrb_funcall_argv and mrb_funcall_with_block to take mrb_sym as a method name

src/re.c

@@ -76,7 +76,7 @@ mrb_reg_s_new_instance(mrb_state *mrb, /*int argc, mrb_value *argv, */mrb_value
   re->ptr = 0;
   re->src = 0;
   re->usecnt = 0;
-  return mrb_funcall_argv(mrb, mrb_obj_value(re), "initialize", argc, argv);
+  return mrb_funcall_argv(mrb, mrb_obj_value(re), mrb_intern(mrb, "initialize"), argc, argv);
 }
 
 mrb_value