fix: Handle SIGTERM more gracefully in watchmedo

[maybe-sybr]

This fixes some misbehaviour where the child process could be orphaned
if watchmedo received multiple SIGTERMs causing the stop() call to be
interrupted. By raising a semantic exception after neutering the signal
handler, we give ourselves a better chance of killing the child.

[BoboTiG]

Hello @maybe-sybr,

Thanks for the patch 💪
Would that fix #543?

[maybe-sybr]

It sounds very similar but I think my change would only fix the behaviour for repeated SIGTERMs and repeated SIGINTs would still misbehave, The KeyboardInterrupt which would get raised by a SIGINT will still be handled in observe_with() which waits for the observer to join and then returns to my diff in auto_restart which will stop the handler and therefore the child - but that could easily get hit by another SIGINT or some other angry signal (e.g. KILL) and break as it did before.

Having looked through this a bit more, I think my diff is somewhat incomplete anyway. By not pivoting to using the semantic exception everywhere, the behaviour is inconsistent and as an example, the observer thread is not stopped as expected since we no longer raise the expected KeyboardInterrupt. I think I can improve the behaviour as well as fixing #543 by updating the diff to do this. I'll work on it now and get a diff up shortly/follow up in an edit.

[maybe-sybr]

@BoboTiG - the new diff fixes #543 from what I can tell. I've only sanity tested it manually on Linux but IIUC since we're limitiing ourselves to catching TERM and INT, it should work fine on Windows. I've also made a small doco change to discourage just catching KeyboardInterrupt in downstream code - lmk if you'd like me to remove that from the changeset prior to merge.

[BoboTiG]

Thanks a lot, that's perfect!

May I ask you to update the changelog + add youself to the line about our beloved contributors?

[maybe-sybr]

Done, @BoboTiG - lmk if you need anything else from me. And thanks for being so responsive!

[BoboTiG]

Thank you for yours :)