Previously this would cause an assertion failure when checking the paths
of exported objects, as it would try to check that their paths started
with ‘//’ due to mishandling the root object case.
Includes a unit test.
https://bugzilla.gnome.org/show_bug.cgi?id=761810
Allow GDBusObjectManagerClient to work on peer to peer DBus
connections. Don't require that a unique bus name is available
for the object manager, if the owned bus name is NULL.
https://bugzilla.gnome.org/show_bug.cgi?id=686920