BF: fix multiskip from setup_modules import

The import of everything from the ``dpy`` module pulled the
``setup_module`` optional import test guarder, causing other modules,
such as ``io``, skip tests with a confusing message about ``tables``.

Stop importing ``setup_modules`` into ``io`` namespace, and make test to
make sure we don't do it again.
Merge pull request #151 from matthew-brett/stop-setup-modules-spreading

BF: fix multiskip from setup_modules import