before closing debugger window in IDLE process.

debugger is active (15347); b) closing the debugger with the [X] button
(15348); and c) activating the debugger when already active (24455).
The patch by Mark Roseman does this by making two changes.
1. To suspend and resume the gui.interaction method, use the tcl vwait
mechanism interded for this purpose instead of root.mainloop & .quit.
2. In gui.run, allow any existing interaction to terminate first.

See https://github.com/python/asyncio/pull/295 for details

not to IDLE itself.

Don't fallback to PyDict_GetItemWithError() if the hash is unknown: compute the
hash instead. Add also comments to explain the optimization a little bit.