bpo-43737: More useful documentation on behavior of % when divisor is negative

[TonyFlury]

… divisor.

https://bugs.python.org/issue43737

[terryjreedy]

Conflict is trivial and easy to fix. I did not do it because A. Tony needs to learn, and B. PR has other changes, not related to issues, and needs to be cleaned up or redone. I expect the latter will be needed.

[TonyFlury]

Withdrawing pull request - will try again once I understand what I did wrong ....

[terryjreedy]

Before you delete the issue-43737 branch, you can check it out and open the files with the changes you wrote. The editor should keep the copy even when you checkout master (and update it!) and delete this branch. If the branch version of the file has both good and bad changes, open the master version in a 2nd editor and copy and paste the good changes into that. (If you are not using IDLE otherwise, it will serve as editor 2.)

After pushing a revised or new branch, and pushing the black on white [ New pull request] on github, but before pushing the green button that 'publishes' the proposed PR, look at all the files listed and the diff for each to make sure the PR has all and only the changes intended and written by you for the issue.