Trying to pip install onctuous with local downloaded files fails as the setup_requires force to download the dependencies.

Moving real deps to install_requires let the package management tool deal with dependencies.

For example those commands should not try to download dependencies:

pip install --no-deps --download /tmp onctuous
pip install --no-deps --no-index --find-links=/tmp onctuous

It's useful when trying to get a reproductible setup for automated production environments