Shutdown subprocess debugger and associated Proxies/Adapters when closing

the Idle debugger.

M PyShell.py       : Call RemoteDebugger.close_remote_debugger()
M RemoteDebugger.py: Add close_remote_debugger(); further polish code used
                     to start the debugger sections.
M rpc.py           : Add comments on Idlefork methods register(), unregister()
                     comment out unused methods
M run.py           : Add stop_the_debugger(); polish code