mail.outbox is a property available just in the mail module
Merge branch 'master' of github.com:mariocesar/sorl-thumbnail

* 'master' of github.com:mariocesar/sorl-thumbnail:
  Duh!
  Added coverage configuration file and command tests
  Tests for descriptor leaks
  Fix descriptor leak in convert engine
  Add coveralls badge to readme
  Add reporting coverage to coveralls
  Py3 style print()
  Fix THUMBNAIL_PRESERVE_FORMAT with non-ascii filenames.
  allow flatten of thumbnails