Events server should raise if port is occupied with something that is not another events server.

The events server runs by default in port 8090. If that port is not free, it will mistakenly think that there's already a server running.

Code has to be improved so the server can detect if whatever is running on that port is indeed another events server or something else.

(from redmine: created on 2013-07-24, closed on 2013-07-25, relates #3275 (closed), relates #3276 (closed))