Add backports-sloppy recipe

Configures squeeze-backports-sloppy suite on Squeeze:
  http://backports.debian.org/Instructions/#index4h2

On Wheezy issues an warning as wheezy-backports-sloppy will be created
only around Jessie freeze.

In all cases also includes the `debian::backports` recipe.
Merge pull request #8 from tmatilai/backports-sloppy

Add backports-sloppy recipe