Display order fix on page duplication

Fixes the display ordering when a page is duplicated.

See:
http://www.concrete5.org/developers/bugs/5-6-3-1/sitemap-scrambles-page-order-after-10-pages-copied/
http://www.concrete5.org/developers/bugs/5-6-3/sitemap-scrambles-page-order-after-10-pages-copied/