`wpdb::prepare()` supports %s, %d, and %F as placeholders in the query string. Any other non-escaped % will be escaped. Merges [41496] to 4.7 branch. git-svn-id: https://develop.svn.wordpress.org/branches/4.7@41498 602fd350-edb4-49c9-b593-d223f7449a82