Themes: Always include the current theme in the list, even if it is not allowed.

see #25948.

Built from https://develop.svn.wordpress.org/trunk@26529


git-svn-id: http://core.svn.wordpress.org/trunk@26422 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Heartbeat: update wp-auth-check to use the new "connectNow()" method after a successful login, see #25073.
Built from https://develop.svn.wordpress.org/trunk@26530


git-svn-id: http://core.svn.wordpress.org/trunk@26423 1a063a9b-81f0-0310-95a4-ce76da25c4cd