Make sure each Disqus thread is associated with official URL.

For some reason Disqus doesn't seem to ignore URLs outside of the configured root domain for the discussion, so test server and spam server domains appear to be the canonical source for comment threads.

We can't do much about the spam servers, but this change should at least stop the test server from appearing.

The change always constructs a www.cappuccino-project.org disqus_url.