With this API, a client can query IPv6/IPv4 information outside re6stnet/babel
for reporting.

The API considers that the email is unique, else it returns the first
occurrence. For SlapOS integration, it is more than enough to consider
that email will not be repeated.

    addToken, isToken and DeleteToken are introduced to manage tokens created
    by other system (like SlapOS for example).

If token is present, raise conflict instead loop until timeout.

This is a useful class that can be used for other reasons.

Which happens when only re6stnet is restarted. The DIF must even be recreated
if the local certificate has changed, so that we can reconfigure the shim DIF.

Commit 6c4a5443 fixes a routing issue and
as usual, all nodes without exception must either route correctly or die:
in the future, we may want to force all nodes to upgrade.

"passive mode" means that re6stnet is configured to not create OpenVPN tunnels.

With :Author:, people may think I am the only author (which is not the case,
as shown by the Git history), whereas I just wanted to specify who is the lead
developer, i.e. the person to contact. And it's not a place to list here people
that are not involved anymore in the project.

- registry: make --dh mandatory
- node: retry if the registry returns nothing (instead of writing an empty file)

I forgot the case where 'config' has slightly different schema.
Now, we don't have any old network left to upgrade.

The presence of /lib/systemd/system/*.service files masked the fact that the
/etc/init.d/ scripts were enabled, and services were not enabled under
systemd (no symlink in /etc/systemd/system/multi-user.target.wants/).

Reverting commit 4c2284e2 partially is the
easiest way to handle the case of OS upgrade (with a switch to systemd).

This fixes a regression caused by commit
  8df410f7