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

props ounziw.
fixes #25604.


git-svn-id: https://develop.svn.wordpress.org/trunk@27073 602fd350-edb4-49c9-b593-d223f7449a82
Add a comment for [27073] as someone will inevitably complain it is tricked by % in a string. see #25604.


git-svn-id: https://develop.svn.wordpress.org/trunk@27074 602fd350-edb4-49c9-b593-d223f7449a82