bpo-38691 Added a switch to ignore PYTHONCASEOK when -E or -I flags passed (#18314)

* Hard reset + cherry piciking the changes.

* 📜🤖 Added by blurb_it.

* Added @vstinner News

* Update Misc/NEWS.d/next/Library/2020-02-11-13-01-38.bpo-38691.oND8Sk.rst

Co-Authored-By: Victor Stinner <vstinner@python.org>

* Hard reset to master

* Hard reset to master + latest changes

Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>
Co-authored-by: Victor Stinner <vstinner@python.org>