Firmata EthernetClient support

Tested on an arduino uno R3 and an arduino ethernet shield r3.  I attempted to test with a leonardo and the same shield but I could not get it to work, possibly because of a compatibility issue http://arduino.cc/forum/index.php?topic=112141.0   . At one point I was playing with the idea of having a ping/heartbeat command which would execute on an interval to check if the board is still connected.  This version does not have this and is working fine but does anyone think its worthwhile to implement a ping command?