Creating Display() fails with "Xlib.error.DisplayConnectionError: Can't connect to display ":0": b'No protocol specified\n"

After a recent dist-upgrade on vivid the following code now raises an exception:

 $ python3 -c "from Xlib import display; display.Display()"

Error:
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/usr/lib/python3/dist-packages/Xlib/display.py", line 80, in __init__
    self.display = _BaseDisplay(display)
  File "/usr/lib/python3/dist-packages/Xlib/display.py", line 62, in __init__
    display.Display.__init__(*(self, ) + args, **keys)
  File "/usr/lib/python3/dist-packages/Xlib/protocol/display.py", line 129, in __init__
    raise error.DisplayConnectionError(self.display_name, r.reason)
Xlib.error.DisplayConnectionError: Can't connect to display ":0": b'No protocol specified\n'

This code was working fine before the dist-upgrade.

Package version is: 0.14+20091101-1ubuntu2 what's odd is that this hasn't appeared to have changed since the dist-upgrade.

This issue is causing all autopilot tests run on the desktop to fail (see: https://bugs.launchpad.net/autopilot/+bug/1432700)