Transactional Refinery

Talk about serendipity: I was just thinking about data transactions for Refinery, and now there's a data manager interface I can implement. It's hard to keep up with the rush of fresh ideas coming out of Repoze.

WSGI aside, I think this would be a smooth transactional API:

>>> w = refinery.workspace('/tmp/data')
>>> collection = w['places']
>>> transaction = collection.begin()
>>> collection.features.append(feature)
>>> transaction.commit() # write to disk

Use an OGR in-memory feature store or new Python structure for uncommitted features? That I don't yet know.