When an HTTPS request to api.wordpress.org fails, try an insecure HTTP request and issue a warning.

Certain versions of cURL appear to claim OpenSSL support but fail to work. We need to not trap users on older versions while we work this out, and instead fall back to an insecure request.

see #25716 for trunk.

Built from https://develop.svn.wordpress.org/trunk@25956


git-svn-id: http://core.svn.wordpress.org/trunk@25915 1a063a9b-81f0-0310-95a4-ce76da25c4cd