autopilot tests fail on wily (backend.introspection_iface.GetState("/") returns an empty list)

[Brendan Donegan]

The autopilot tests are failing on wily, with the following error:

Traceback (most recent call last):
  File "/home/brendand/src/autopilot-gtk/tests-wait-not-visible/tests/autopilot/tests/test_widget_tree.py", line 34, in setUp
    self.app = self.launch_test_application(test_app, app_type='gtk')
  File "/usr/lib/python2.7/dist-packages/autopilot/testcase.py", line 264, in launch_test_application
    return self._launch_test_application(launcher, application, *arguments)
  File "/usr/lib/python2.7/dist-packages/autopilot/testcase.py", line 367, in _launch_test_application
    application_name=application_name,
  File "/usr/lib/python2.7/dist-packages/autopilot/introspection/__init__.py", line 187, in get_proxy_object_for_existing_process
    return _make_proxy_object(dbus_addresses[0], emulator_base)
  File "/usr/lib/python2.7/dist-packages/autopilot/introspection/__init__.py", line 457, in _make_proxy_object
    data_source
  File "/usr/lib/python2.7/dist-packages/autopilot/introspection/__init__.py", line 618, in _get_proxy_object_class_name_and_state
    state = backend.introspection_iface.GetState("/")[0]
IndexError: list index out of range

so it seems that backend.introspection_iface.GetState("/") is returning an empty list. This is using the updated version of xpathselect in -proposed (1.4+15.10.20150817.1-0ubuntu1)