SERVER-15789 Close record stores before shutdown or drop

This pleases any storage API that requires there to be no open handles to storage
abstractions on shutdown or drop.

https://jira.mongodb.org/browse/SERVER-15789
I think I did a bad job at porting this patch over to the new refactored code that does drop as part of a RecoveryUnit::Change

The close is probably not needed anymore because for both dropOnRollback and dropOnCommit the entry gets deleted which deletes the underlying record store and calls the destructor, to your point.