"issue28082: use IntFlag for re constants" by Ethan Furman.

The re module is not more used in the site module and so adding "import enum"
to re.py doesn't impact python_startup benchmark anymore.

Patch by Matthieu S.

with a cosmetic change to add a commit message with the issue number,
missing from the previous two commits.

Patch by Gareth Rees.

parse_constant doesn't get called on 'null', 'true', 'false' since 3.1/2.7.

parse_constant doesn't get called on 'null', 'true', 'false' since 3.1/2.7.

parse_constant doesn't get called on 'null', 'true', 'false' since 3.1/2.7.

when decode astral characters.

when decode astral characters.

when decode astral characters.

when decode astral characters.

when decode astral characters.

(e.g. on Android).

(e.g. on Android).

(e.g. on Android).