Improve management command to clear or clean kvstore
Merge branch 'master' of github.com:mariocesar/sorl-thumbnail

* 'master' of github.com:mariocesar/sorl-thumbnail:
  Adds another possible exception to is_valid_image
  is_valid_image does something useful now in wand-engine
  Passing cropping tests
  Update documentation, test runner and little fix in cropping
  New engine for wand
Merge branch 'master' of github.com:mariocesar/sorl-thumbnail

* 'master' of github.com:mariocesar/sorl-thumbnail:
  Recommend Pillow instead of PIL
Update tests and fix missing SECRET_KEY in settings