Return false from wp_get_referer() and wp_get_original_referer() if called before wp_validate_redirect() is defined.

Merges [25399] and [25400] to the 3.6 branch.
see #25294.

Built from https://develop.svn.wordpress.org/branches/3.6@25401


git-svn-id: http://core.svn.wordpress.org/branches/3.6@25332 1a063a9b-81f0-0310-95a4-ce76da25c4cd