Consistently use chat.freenode.net

* freenode.org is a redirect to freenode.net.
* chat.freenode.net is now the canonical entry point,
  replacing irc.freenode.net.

See also http://freenode.net/irc_servers.shtml
Merge pull request #264 from Krinkle/irc-freenode-refs

Consistently use chat.freenode.net