M PyShell.py
M ScriptBinding.py
M rpc.py
M run.py

Clean up the way IDLEfork handles termination of the subprocess, restore
ability to interrupt user code in Windows (so long as it's doing terminal
I/O).

1. Handle subprocess interrupts in Windows with an RPC message.
2. Run/F5 will restart the subprocess even if user code is running.
3. Restart the subprocess if the link is dropped.
4. Exit IDLE cleanly even during I/O.
4. In rpc.py, remove explicit calls to statelock, let the condition
   variable handle acquire() and release().