Fix broken in-memory 'startswith' filtering

_normalize_lookup_value returns a tuple for 'startswith' queries, not a
string as was assumed.
updated django-permission-backend-nonrel url
Merge pull request #32 from django-nonrel/in-memory-startswith

Fix broken in-memory 'startswith' filtering
Modify NonrelInsertCompiler to support bulk inserts, remove XMLField usage, use model._state.adding instead of model._entity_exists, and other minor changes
Remove XMLField reference
Merge branch 'features/django-1.4' of github.com:django-nonrel/djangotoolbox into merge

Conflicts:
	djangotoolbox/db/base.py
	djangotoolbox/db/basecompiler.py
	djangotoolbox/fields.py