Do not assume a cart has its customer set.
Merge branch 'master' of http://github.com/visualspace/django-shopkit
Made using a Customer model optional, allowing for simpler Order models where customer management is not required.
Forgot one in last commit.
Made sure the ShippedOrderBase stuff doesn't assume a shipping_address as this makes no sense for simpler order models or when no automatic selection of methods is used.
Made ADDRESS_MODEL not required anymore.
Merge remote branch 'origin/cosmania' into sacksioni
Merge remote branch 'origin/sacksioni'
Forgotten abstract = True, whitespace removal.
Updated CartAddBase view for updated cart API

Fix for #1 and whitespace removal.
PEP8, cleaner logging parameter substitution.
Set abstract = True for Customer*Base classes
More PEP8 cleanup.
Use clean() instead of save() for setting ordering

This fixes a bug with django-mptt where it 
expects the ordering to be set when save() is
called.

Reference:
https://docs.djangoproject.com/en/dev/ref/models/instances/#django.db.models.Model.clean
Whitespace cleanup, clean() before save in tests
Merge remote-tracking branch 'origin/sport81' into cosmania

Conflicts:
	shopkit/core/models.py