Binding to random port

[the20login]

There are cases when you would like to bind to random port.
Intuitive way to do so is to set port to zero.
Unfortunately, there is no way to extract real port. API method just return configured port instead of getting it directly from socket.

I, personally, would prefer separated method (like "bindPort()") instead of altering current method behaviour. This also helps to maintain backward compatibility.

[the20login]

I'm ready to write PR, if you point me to preferred API (alter current method or add new one).