Bug#733489: python-apt: Improve 'Dependency' and 'BaseDependency' to get target package versions that satisfy dependencies

[Michael Schaller <michael@5challer.de>]

A few comments on the patches:

1) tests/test_pep8.py
Can you document in a comment or docstring why you ignore certain issues 
and what these issues are? This should help readers to better understand 
what the test does and more importantly what it ignores.
Furthermore do you plan to reduce the number of ignores in the future? 
If so you should add a TODO for yourself.

2) tests/test_pep8.py
Can you use instead of 'self.assertEqual(res, 0)' a better fail message 
like you did in 'tests/test_pyflakes.py'?

3) tests/test_pyflakes.py
You don't need the 'from __future__ import print_function' import with 
Python 3.

4) debian/control (nitpick)
I prefer to sort dependencies alphabetically.

5) .travis.yml
I would really like to see a rather lengthy comment in the beginning of 
the YAML file to explain what purpose it serves and what it does. I also 
think you should give a link here and that you should explain what 
should happen after Trusty. Maybe it would be even better to use SID 
instead of Trusty.

6) .travis.yml
Why do you run './debian/rules binary' and not 'dpkg-buildpackage'?

7) .travis.yml
Why not also ensure here that Lintian and if possible piuparts have no 
issues with the newly built package?