Fixup tests.suite() for 'setup.py test'

When trying to test my changes, I wasn't sure how to execute tests. 

Originally 
<pre>
python setup.py test --with-cython
...
----------------------------------------------------------------------
Ran 0 tests in 0.000s

OK
</pre>

tests.suite() returns an empty test suite. This diff fixes it and integrates the doctests that were defined in the bottom of test.py.   I only called methods known to exist in python2.5

After
<pre>
----------------------------------------------------------------------
Ran 127 tests in 2.122s

FAILED (failures=1)
</pre>

The failure Is known (FAIL: test_eval_error_message_decoding (lupa.tests.test.TestLuaRuntime)) because I am using Lua 5.1

If the new behavior of test.py is too much a change we could always swap out the bottom of the file for
<pre>
if __name__ == '__main__':
    from . import suite
    unittest.TextTestRunner(verbosity=2).run(suite())
</pre>