Display which incoming port is being used

[mitar]

It seems that dat can automatically start using a non-default ports if cannot get a default port. For example, if I run multiple instances of dat share on my machine, the first will use the default port, but other instances will not. But this means that without opening a firewall for those random ports now used by other instances, peers are unable to connect.

I think that dat should print out that it is using an alternative port. Or it should complain and exit and require user to specify a port on their own using the --port argument.

[pfrazee]

Seems like a good idea to me