Bug#780929: Talked to the pythondialog maintainers

[Francois Marier <francois@fmarier.org>]

I should perhaps mentioned that I have talked to the pythondialog (the 
Python 3 only version) maintainers in Debian and they were supportive of 
my upload of the Python 2 backport.

I expect to be able to deprecate and remove this package once 
letsencrypt adds support for Python 3, but for now it's a hard 
dependency.

Francois