Probably a fix of issue #87

Actually, nothing really bad happens here, but the message itself is very confusing. After ~2 hours of investigation I found it very difficult to get rid of the message correctly. So, I decided to try just sending `UserJoin` from `JabberProtocol` to the message handler on joining the room. Hope it doesn't break anything. At least, on my local machine it works fine.
I don't really like your solution. Maybe just construct MucMessageListener with predefined collection of users including horta? Or somehow query Smack for self-nick and fill in the collection from it? I'm sure there are plenty of solutions which do not include such a hacks.

I recommend you to reconsider this patch.