Unslash in the time-format and date-format ajax endpoints.

props GregLone.
fixes #27216.

Built from https://develop.svn.wordpress.org/trunk@27305


git-svn-id: http://core.svn.wordpress.org/trunk@27158 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Themes screen: Clicking back through history should properly close the overlay.

props gcorne.
fixes #27198.

Built from https://develop.svn.wordpress.org/trunk@27306


git-svn-id: http://core.svn.wordpress.org/trunk@27159 1a063a9b-81f0-0310-95a4-ce76da25c4cd