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

https://reproducible-builds.org/

Anyway, OpenVPN >= 2.3 was already missing on Squeeze, even via backports.

- Suse wants units in /usr/lib/systemd/system
- respect system-preset

debian/rules is split into reusable parts for SlapOS-based packages.

Unexpectedly, and contrary to 'dot', Graphviz does not draw it with penwidth=0
(without, that of the other side is striked). And anyway, we can just look at
the label to see if there's a route.

iproute now shows the name of the paired interface for type veth. For example:

  172: NETNSif-476f004@NETNSif-476f003: ...

When 10.42.3.1/24 was configured on 'lo', the kernel accepted packets to
any ip of 10.42.3.0/24, instead of only 10.42.3.1