OpenSSL::SSL::SSLError when talking to github

Running the following code on JRuby:

``` ruby
require 'open-uri'
open "https://api.github.com"
```

Results in a `OpenSSL::SSL::SSLError: certificate verify failed`.

Issue appears on 1.6.7.2, 1.7.0-preview1 and head, both in 1.8 and 1.9 mode, both on OSX 10.7 and Ubuntu.

See also http://travis-ci.org/#!/rkh/gh/jobs/1441018
