It still doesn't build:

> I fixed the typo. What is the error message?

<pre>
reading sources... [ 35%] modules/classes                                       
Exception occurred:
  File
"/home/varoquau/dev/scikit-learn/doc/sphinxext/numpy_ext/docscrape.py",
line 212, in parse_item_name
    raise ValueError("%s is not a item name" % text)
ValueError: :ref:`examples/plot_polynomial_regression.py is not a item
name
The full traceback has been saved in /tmp/sphinx-err-RdTJcn.log, if you
want to report the issue to the developers.
</pre>

I am not convinced that you can put rst syntax in a numpy docstring
"seealso" block. I wonder if it is not only symbol names.