Inline documentation improvements for wp-includes/user.php.

Props morganestes, SergeyBiryukov.
Fixes #26148.

Built from https://develop.svn.wordpress.org/trunk@27353


git-svn-id: http://core.svn.wordpress.org/trunk@27204 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Additional clarification for wp_authenticate_cookie() parameters.

fixes #26148.
Built from https://develop.svn.wordpress.org/trunk@27354


git-svn-id: http://core.svn.wordpress.org/trunk@27205 1a063a9b-81f0-0310-95a4-ce76da25c4cd