setup.py: Enable "testing" setuptools extra.
setup.py: Enable "testing" setuptools extra.

Enables things like:

pip install -e .[testing]

genixpro/formencode,genixpro/formencode,jvanasco/formencode,formencode/formencode,jvanasco/formencode,systemctl/formencode,genixpro/formencode,formencode/formencode,formencode/formencode,systemctl/formencode,systemctl/formencode,jvanasco/formencode