tox.ini: Correct name of dep from "py" => "pytest"
tox.ini: Set sitepackages=True for py25 so that it can use globally
installed "ssl" module
Makefile: Work around that tox removed toxbootstrap.py
Remove `pip install tox`
Merge pull request #23 from msabramo/tox-tweaks

Tox tweaks

toxbootstrap.py is no more.