M Bindings.py

M PyShell.py
M config-keys.def
M configHandler.py

1. Clear any un-entered characters from input line before printing the
   restart boundary.
2. Restore the Debug menu: There are now both Shell and Debug menus.
3. Add Control-F6 keybinding to Restart Shell.
4. Clarify PyShell.cancel_check() comment.
5. Update doc string for Bindings.py and re-format the file slightly.