A small change to simplify the methodology of selecting mock resultsets from MockDataProviders

The new abstract class SelectableMockDataProvider and new class SelectableMockConnection extend the functionality of the existing MockDataProvider and MockConnection so that just prior to running a query from test code, the test code can select the appropriate results by calling SelectableMockConnection.setSelector(int). This integer value is then available to be used by the SelectableMockDataProvider implementation in order to choose the appropriate resultset to be returned for subsequent queries.