Merge the should_auto_update() and can_auto_update() methods. see #22704.


git-svn-id: https://develop.svn.wordpress.org/trunk@25815 602fd350-edb4-49c9-b593-d223f7449a82
Update the banner for update-core.php that tells users they are set up for security updates to happen in the background.

"This site is set up to install security updates of WordPress automatically. Cool!"

Checkmark is a placeholder; we'll tinker with this further today.

see #22704.


git-svn-id: https://develop.svn.wordpress.org/trunk@25816 602fd350-edb4-49c9-b593-d223f7449a82