csm-manager.c: Unset WAYLAND_DISPLAY during shutdown in a wayland
session.
This and others need to be cleared after a wayland session so
systemd doesn't pass them to the next session.
This is performed by others using systemd unit parameters, but we
don't currently use systemd for this. https://gitlab<email address hidden>?ref_type=heads#L26
session-quit: Use a unique dialog server address for each session.
This was preventing the logout dialog for subsequent users logged
in, as it would attempt to connect to the original user's server
(and be denied).
- A unique address will be generated at startup, and passed to
the dialog when it is launched.
- Log output from the c-s-owned dialog process when debugging is
enabled.