Rename distro/ to systemd/. Systemd service files are not supposed to be distribution-specific.
Make systemd service file handling identical to tinc 1.1. This removes hardcoded paths from systemd unit files, and sets the default systemd unit path to ${libdir}/systemd/system. The configure option is now renamed to --with-systemd[=PATH]. These changes now also ensure that make distcheck runs without any errors. Closes #160 on GitHub.
Ensure the service files are in the tarball.
Add systemd service files.