Tests should be run against current version of django-wiki, not old version!
Updated dependencies in tox.ini to latest supported versions of Django
Get tests to run under Django 1.4 and 1.5, but without duplication on 1.6 and later
Pulled out some useful base classes for test cases
Fixed bug with caching that was causing a test to fail.

Running Article.clear_cache() on deleting isn't enough to properly clear the
cache.  This is because get_cache_key() can return different values - so if
you 1) create an article 2) then modify it 3) then delete, the cache of
content after 1) is not cleared by Article.clear_cache() after 3).

Therefore, when saving, we also clear the instance cache. This is more
robust, and means we also don't have to explicitly delete Articles in test
tearDown.

This bug shows up particularly in tests, due to the increased possibility of
IDs being re-used.
Removed stray debugging print statement
Fixed uploading of attachments using Python3

Previously it was failing with "TypeError: Unicode-objects must be encoded
before hashing" when taking the md5 of a Python3 str object.
Merge pull request #332 from spookylukey/fix_upload_for_python3_rebased

Fix upload for python3 rebased