Unable to use AsyncPreview.preview_ready() from python

[Michal Hruby]

When using AsyncPreview in python:

>>> from gi.repository import Unity
>>> a = Unity.AsyncPreview.new()
>>> p = Unity.GenericPreview()
>>> a.preview_ready(p)

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.7/dist-packages/gi/types.py", line 47, in function
    return info.invoke(*args, **kwargs)
gi._glib.GError: Could not locate unity_async_preview_preview_ready: `unity_async_preview_preview_ready': /usr/lib/x86_64-linux-gnu/libunity.so.9: undefined symbol: unity_async_preview_preview_ready

[Michal Hruby (mhr3)]

As a workaround `a.emit("preview-ready", p)` works.