It's potentially confusing to have it default to a value as you might
miss this in your project.

This involves:
* Better checkout templates
* Updated availability logic for products with no stock
* Updated dashboard templates

This is a major clean-up of offers, tidying up the implementations and
rewriting the test suite.  This should also clean up some edge cases
around the use of max_affected_items.

* replaces all occurences of ``datetime.now()`` with
    ``django.utils.timezone.now()`` which returns aware or naive
    datetimes based on ``USE_TZ``
* increases ``South`` version to 0.7.6 in dependencies to make
    aware datetimes work in migrations.
* Oscar's sandbox is now configured to use aware timezones by
    default

Turns out this is a bit confusing.  Better for it to do nothing by
default and this behaviour can be enabled when it is needed.

Change to products URL was not picked up here.

Now using --spec format which is more readable (most of the time).

They weren't applying to lines properly.  Fixed with test.

Also tidied up test case for basket model

* Less DB queries
* Added basic tests

This avoids conflicts with other libraries that use the same trick for
extending templates.

The validation on the stockrecord form needed to be removed to allow
group products to be created, which don't have stock records.

Also added tests for vouchers

They now must have a title

To work around MySQL bug with fields of > 255 chars not being allowed to
have unique indexes.

Plus tweaks to test method names

Also split them into unit and functional tests.