[issue8538] Add FlagAction to argparse

[Rémi Lapeyre]

Change by Rémi Lapeyre <remi.lapeyre at henki.fr>:


----------
keywords: +patch, patch, patch
pull_requests: +10987, 10988, 10989
stage: needs patch -> patch review

_______________________________________
Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue8538>
_______________________________________