For cases where NM may run without a bus daemon in root-only
environments, like an initramfs.  For disconnection, since private
connection just get a disconnect message instead of NameOwnerChanged
signals broadcast by a bus daemon, just synthesize the NameOwnerChanged
signals using our fake owner name.  It's just easier to do this rather
than modify any code that cares about disconnects.

Note that the new private socket is only enabled if built with
dbus-glib >= 0.100 as there are bugs in previous versions in the
implementation of dbus_g_proxy_new_for_peer() which clients must
use to talk to the private socket.