Always create a library instance

Tests started failing because the storybase_i18n template tag library
doesn't always contain a ``register`` variable instantiated with
``register = Library()``. This should always happen, even if the rest of
the template tag implementation doesn't get executed (because it's a
backport that's only needed for Django 1.3).
More generic versions for Django

The version spec strings now reflect any version within the supported
major versions instead of a specific minor version. This way, people will
always get the most recent version of a supported Django when doing a new
install, and the Travis build will always get the latest supported Django.

See http://pythonhosted.org/distribute/pkg_resources.html#requirements-parsing
Major version, not minor version

Rename the pip requirements file for Django 1.3 dependencies to reflect only
the major version since we want users to install the most recent supported
version.
Update changelog for 0.5.5 version bump