IO Error if smack cant use port for local proxy

I am closing this and opening a new documentation task to address this. Although it is documented in the code, it should also be added to the File Transfer documentation.

I am not sure about this issue and fix.

1. The "isSetUp" bool is not needed. Better find some action (e.g. throw an exception) in the else case of "if (this.serverSocket != null)".
2. It would be much easier to just set the standard Socks5 Port to "-7777" in SmackConfiguration.java. That would result in the same behavior as this patch, without adding more LOC.

So to anyone who likes to run more than one instance of Smack on an host: Simply set the default port to a negative number. This is the workaround for this bug. Note that this is also documented (I am sure Henning had this in mind when he implemented this).

If a user try to run two clients on the same machine with local proxy, the second client can't establish a socket to the same port the first client is using (7777 per default).
If the default port is less then zero, smack will try to find a port which is not used. If the default port is above zero, smack want to use the specific port which can throw a IO Exception if the port cant be used.

This patch make smack to search for a free port if the default port cant be used.