Show testsetup code in rendered docs.

For `testsetup`, Sphinx does not show code in the output: http://www.sphinx-doc.org/en/stable/ext/doctest.html#directive-testsetup This commit fixes that issue, although duplicates code. I'll submit a feature request to https://github.com/sphinx-doc/sphinx/ Fixes #2670
(cherry picked from commit 2612de2)