domain_menu() can cause recursion

Because of how hook_domain_batch is structured, the menu hook invokes that code and it executes, which should likely be changed.

In the meantime, you can see endless recursion under the following conditions:

* Domain Conf is installed.
* Cache is fully cleared.
* Menu module is installed.

The error is Fatal error: Maximum function nesting level of '100' reached, aborting! in /shared/www/includes/database/query.inc on line 325

What happens is that domain_conf_domain_batch() calls menu_parent_options, which can hit an endless loop.