!act #3490 Changed the callback to SocketOption to accept a channel instead of a Socket, this allows for using the nio features.

For example in Java 7 you can now join a multicast group:

case class JoinGroup(group: InetAddress, networkInterface: NetworkInterface) extends SocketOption {

  override def afterConnect(c: DatagramChannel): Unit = {
    c.join(group, networkInterface)
  }
}

  IO(Udp) ! Udp.Bind(self, new InetSocketAddress(MulticastListener.port),
    options=List(ReuseAddress(true),
      JoinGroup(MulticastListener.group, MulticastListener.interf)))

Other minor changes:

 - changed all methods in SocketOption to take a Channel instead of a Socket.  The socket can be gotten from the Channel but not the reverse.
 - all methods that are called before the bind are now called beforeBind for consistency.
 - All network connections now call the beforeBind and afterConnect.