In SERVER-38071 we need to explicitly abandon a snapshot after doing a findOne on the authz data for mongod, but there is no way to know whether you already have a snapshot to begin with. This should be okay since authz checks are the first thing we do, but it would be nice to be able to check that assumption and ensure programmatically that we are not abandoning a snapshot that a user query needs.

geert.bosch told me to file this ticket to lift the inActiveTxn() function into the RecoveryUnit interface.