- add Cnf-Visible-Pkgname hint to ensure command-not-found recommends
      installing "python" instead of "python-minimal" when it is missing.

  * README.Debian: Reference 2.7 and point to the python3 package for the
    Debian Python Policy.
  * Mark python-examples as M-A: foreign.

    against people fiddling around with the python symlink or having a 
    python3 installed as python in /usr/local. LP: #1715062.

    Closes: #872421.

  * Bump debhelper version.

Add short section on setuptools

This improves the situation because it eliminates the constraints on packages
outside of pip, and leads to a reduction in <pkg>-whl packages in the archive.