Cannot add nodes to non-og_menus

og_menu_form_node_form_alter lets users with 'administer menus' permission choose from the non-og_menus available for the content type from a node form.

Unfortunately, the validation in og_menu_node_form_validate does not allow it, so you just get to choose the option and have the entire page not validate. Or even more fun, add og_menu to an existing site and you can no longer edit any nodes that are in non-og_menus.

The patch makes the validation added only when the user does not have administer menus perm.