Fix for issue #27: add explicit socket close on ABORT

Adds a condition handler that traps ABORT signals and allows `ros_relay` and `ros_state` to properly shutdown and close any open sockets. This solves the issue where sockets on the controller remain in WAITING or OPEN state, confusing the ROS client programs (no data coming in, but still connected, while server programs have already been terminated).

Could potentially create conflicts with old versions of `ros_relay` and `ros_state` as I had to introduce a new variable (`shutdwn_req_`).

Tested on simulated and real R-30iA, HandlingTool V7.70

I'll address this in a later set of changes.