In a recent Slack thread there was confusion about mongodump’s correctness stance in the absence of --oplog.

Specifically, it was unclear that, while mongodump might produce an internally-consistent backup, it can’t be guaranteed without --oplog. We should amend dump/restore’s documentation accordingly, e.g.:

1. Show a warning whenever --oplog is NOT given.
2. Add a “Data Integrity” section to mongodump’s --help and other relevant documentation.