Inline documentation for hooks in wp-includes/update.php.

Props ShinichiN.
Fixes #25467.

Built from https://develop.svn.wordpress.org/trunk@25699


git-svn-id: http://core.svn.wordpress.org/trunk@25614 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Be as sure as possible that WordPress is not under version control when deciding if we should do automatic updates.

see #22704.

Built from https://develop.svn.wordpress.org/trunk@25700


git-svn-id: http://core.svn.wordpress.org/trunk@25615 1a063a9b-81f0-0310-95a4-ce76da25c4cd