As part of WT-1228, we can enable cursor caching for WiredTiger in the integration layer. Originally, we intended to remove the cursor caching done in the integration layer. To get roughly equivalent performance, we should keep the caching at the integration layer (with a much lower count of cursors), and when a session is released, all cursors in the session will be closed. Closing the cursors will cache them in WiredTiger, so that reopens will be quick. Thus, this is called a hybrid scheme. It has the benefit of the original plan that we should be able to immediately drop or verify collections that are no longer in use.