Transport information in SlaveAPI::getBusInfo() for `roscpp` and `rospy` nodes

With the following changes, `roscpp` and `rospy` nodes will append an extra field to `getBusInfo()` response [in [slave XMLRPC API](http://wiki.ros.org/ROS/Slave_API)] to include detailed transport information. The format is as follows:

_CONNTYPE_ connection on port _LOCALPORT_ to [_REMOTEHOST_:_PORT_ on socket  _SOCKETNUMBER_]

e.g.

    TCPROS connection on port 56858 to [127.0.0.1:32993 on socket 10]

- It looks as if `UDPROS` is not completely supported by `rospy`. Therefore no response will be sent by `rospy` nodes using UDP (is it even possible?).

- For `roscpp` and UDP, I could not find a way to reliably determine `remotehost:port`  and `socketnumber` for _subscriber_ links. (_publisher_ links work fine.)

- This PR also adds an extra field to `roscpp` `getBusInfo()` responses to make the length equal to responses sent by `rospy` nodes.  

This is my first time to send pull request to core ROS packages. Any comment or hints is highly appreciated. I am also more than happy to write tests for the new feature if it is required.