Solution:
The error is not with WordPress wanting to connect back to itself securely. It is trying to make a call to https://wordpress.org. The Defines you added are actually making it worse.
define(‘FORCE_SSL_LOGIN’, false);
define(‘FORCE_SSL_ADMIN’, false);
define(‘FORCE_SSL’, false);
define(‘WP_HTTP_BLOCK_EXTERNAL’, false);
I would remove them.
As ot the problem, I seem to remember Andrew Nacin talking about the fact that they were migrating all calls back to wordpress.org to https calls. While it is possible that it is your setup, my guess is that it is your firewall. For some reason it is blocking access to https://wordpress.org. This can easily be verified by checking the firewall logs. If that is the case, you will need to figure out how to allow your site to dial out in order to use the theme and/or plugin installer. Also, you won’t be able to use the automatic updater.
All of these tasks can be done manually, so it’s not the end of the world if you can’t unblock it. But it will be an inconvenience.
HTH,
=C=