please pull my asof() related patches

The first one fixes asof() so that the AsOf attribute is added to the returned objects.

The second will allow passing None to the asof() function, which is equivalent of not using asof at all. This is also possible to add when a list of asof() values are passed, e.g.

v1.PrimaryWorkitems.filter(...).asof("2011-01-01", "2011-02-01", None)

returns 3 sets of data, two for the specific dates, and the third for the actual state.

Please Apply!
Thanks