Throw an incorrect usage notice when the query argument of wpdb::prepare() does not include a placeholder.

props ounziw.
fixes #25604.

Built from https://develop.svn.wordpress.org/trunk@27073


git-svn-id: http://core.svn.wordpress.org/trunk@26946 1a063a9b-81f0-0310-95a4-ce76da25c4cd