It is more efficient to run only one test for Python 2.x and one for
Python 3.x. The full set of tests, including all supported versions
listed in `setup.py` should be run locally at least before
releases. Then we also do coverage tests, pep8 and pyflakes.

The 'run diceware' test should remain until we have some other
regression test for bug #1.

This reverts commit 01f2a328.

Reason: The file list changed in this commit was only for py.test
        to lookup possible test sources (doctests or Python tests).
        Wordlists do not contain tests.

Include wordlist_en.txt via pip install

We now read from already opened file descriptors (in get_wordlist()) only.