RFC: Specifying lists of versions

I didn't make a patch for this one as I don't have a firm proposal.

Currently Python policy says:

Lists of multiple individual versions (e.g.  2.4, 2.5, 2.6) work for `XS-
Python-Version' and will continue to be supported, but are not recommended and
will not be supported by `X-Python-Version' or `X-Python3-Version' after the
Squeeze release.

The dh_python3 and py3versions (I only looked for Python 3 so far) currently
in bzr will error on a list like X-Python3-Version: 3.1, 3.2, 3.3.

Based on Stefano Rivera' analysis, this affects no packages in Sid.  Extending
the same error to X-Python-Version would affect no packages.  

Lists of one or two versions are a bit different.  The Python policy currently
has a two item list as an example, e.g. 2.6, 2.7, so it's quite reasonable for
people to expect lists of one or two items to work.

This affects no Python 3 packages, but a small number of Python packages that
use X-Python-Version (vice XS):

List of two versions:
python-pam
graphviz
rapid-photo-downloader

List of one bare version:
zope2.12
actdiag
mayavi2
wrapitk-python
nwdiag
qpid-cpp
gdcm
blockdiag
openchange
seqdiag
sphinxcontrib-actdiag
sphinxcontrib-seqdiag
stimfit
sphinxcontrib-blockdiag
serna-free
slapos.core

Since the code currently supports lists, my thought it that (for Wheezy at the
very least) allowing a list of one bare python version ought to be allowed for
Python (I don't see a lot of value in changing 2.7 to >= 2.7, << 2.8).

For Python 3, since there's no packages currently affected, I think it makes
sense to eliminate lists entirely and just use ranges. If someone wants to
specify one and only one version, they could use == 3.2 (I need to check if
the code supports this).

Comments?

Scott K