Fix and reenable Python 3.4 tests on Travis

Closes #203

Some background: PEP 453 introduced the 'ensurepip' module to Python 3.4.
'make install' runs 'python3.4 -m ensurepip' which installs setuptools
into site-packages.  Our test suite doesn't like that.  Luckily,
Python's ./configure has an option to disable ensurepip.