Drop Python 2.6 support

We need to bump the version of django-dynamic-fixture to get the test
suite to run under Python 3. They've dropped Python 2.6 support in the
same release.
Upgrade sorl-thumbnail & django-dynamic-fixture for Python 3 support

sorl-thumbnail unreleased version trips when THUMBNAIL_DEBUG isn't set.
I've submitted a pull request to fix it.
Minor test suite fixes for Python 3 compatibility

TestCase.assertEquals (note the s at the end) has been deprecated.
The only failing tests remaining are CSV related, which is not
surprising.
Add Python 3.4 to list of supported Python versions

Tests currently don't pass, but I'm hopeful they will in time for the
release of 0.8.