Manual paging

Jorge, this small change allows for manual paging and throttling.

A new query option manualPage: true enables the paging behavior. In contrast to autoPage, manualPage does not automatically invoke self._innerExecute. Instead, the self._innerExecute is wrapped in nextPage method exposed via the result param in the second, operation status callback.

This means the status callback is invoked at end of each and every page instead of just once after everything has been read. Despite, the caller does know when there's no data left - the nextPage method is absent on the last invoke.

Please merge, or let's get this back to the drawing board and discuss a better manual paging/throttling interface.

Thanks,
-Krassimir