The CreateSession D-Bus API of systemd-logind changed between v44 and
v204 [1]. As result, newer versions of libpam-systemd fail to register a
new session if they talk to the old systemd-logind process.
Restarting systemd-logind.service when upgrading from v44 means we will
lose existing sessions, but as wheezy still has ConsoleKit as default,
this shouldn't matter that much.  Closes: #717403

[1] https://bugs.freedesktop.org/show_bug.cgi?id=67131