Added change log entry for change to Rigidbody::robotnum.
Added change log entry for change to Rigidbody::robotnum.

billhoffman/drake,sheim/drake,billhoffman/drake,sheim/drake,sheim/drake,sheim/drake,billhoffman/drake,sheim/drake,sheim/drake,sheim/drake,billhoffman/drake,billhoffman/drake,billhoffman/drake,billhoffman/drake,billhoffman/drake,sheim/drake