Only sequence of ASCII digits will be accepted as a numerical reference.
The group name in bytes patterns and replacement strings could only
contain ASCII letters and digits and underscore.
It was initially added to support atomic groups, but that
support was never fully implemented, and CALL was only left
in the compiler, but not interpreter and parser.
ATOMIC_GROUP is now used to support atomic groups.
In expression (?(group)...) an appropriate re.error is now
raised if the group number refers to not defined group.
Previously it raised RuntimeError: invalid SRE code.
* Move the code for generating Modules/_sre/sre_constants.h from
Lib/re/_constants.py into a separate script
Tools/scripts/generate_sre_constants.py.
* Add target `regen-sre` in the makefile.
* Make target `regen-all` depending on `regen-sre`.
Serhiy Storchaka
Ma Lin