In `wpdb`, make some things explicitly `public`. Do not set anything to `private`. This would instantly blow up `hyperdb` in the wild.

See #27881, #22234.

Built from https://develop.svn.wordpress.org/trunk@28526


git-svn-id: http://core.svn.wordpress.org/trunk@28352 1a063a9b-81f0-0310-95a4-ce76da25c4cd