Update `chown` to allow setting the owner of a file to a numeric user
ID regardless of whether a corresponding username exists on the
system.
For example,
$ touch f && sudo chown 12345 f
succeeds even though there is no named user with ID 12345.
Fixes#3380.
* chown: support '.' as 'user.group' separator (like ':')
It also manages the case:
user.name:group (valid too)
Should fix:
gnu/tests/chown/separator.sh
`LANGUAGE=C` is not enough, `LC_ALL=C` is needed as the environment
variable that overrides all the other localization settings.
e.g.
```bash
$ LANGUAGE=C id foobar
id: ‘foobar’: no such user
$ LC_ALL=C id foobar
id: 'foobar': no such user
```
* replace `LANGUAGE` with `LC_ALL` as environment variable in the tests
* fix the the date string of affected uutils
* replace `‘` and `’` with `'`
