tests/readlink.py

help: get helptext/ data from `resources` module if available

For PyOxidizer, we need to read configs using the `resources`
module. This patch makes it so we use that module if available
(i.e. Python >= 3.7). It does that by adding a new `open_resource()`
function to our `resourceutil` module.

Tested by running `$PYTHON ./hg help pager` for each $PYTHON in
{python2, python3.6, python3.7}.

Differential Revision: https://phab.mercurial-scm.org/D7622

#!/usr/bin/env python

from __future__ import absolute_import, print_function

import errno
import os
import sys

for f in sys.argv[1:]:
    try:
        print(f, '->', os.readlink(f))
    except OSError as err:
        if err.errno != errno.EINVAL:
            raise
        print(f, '->', f, 'not a symlink')

sys.exit(0)