Resolves#203
Related to pypa/twine#314
This commit adds an ``sh -c`` call, whose argument is the value of the
environment variable ``PYPISERVER_SETUP_CMD``, or ``true`` if that
variable is not set. This was specifically added to enable the
``pre_twine`` environment, which is provided to automatically test
pre-releases of twine, both for our use (e.g. #203) and for the use of
the twine maintainers (pypa/twine#314).
The capacity to specify an arbitrary setup command via an environment
variable may also wind up being useful in other cases in the future.
In addition, the envlist is updated to include only Python versions we
actually support.
This commit also alphabetizes the ``dev.pip`` requirements and rmeoves
specific requirements for testing using Python 2.5 (which we do not test
against anymore).
In addition to including tests from @jameshiebert with slight
updates, I have also resolved an issue with newer versions of twine,
which require an extra parameter in the calls to `upload` and
`register`.
python 2.5 needs an older webob version. so, we add the dependency in
tox.ini. we use tox to run the tests on travis.
remove python 3.3 from travis.yml as it's not there yet.
