Shell outputs diagnostic information in batch mode even with --quiet when talking to older mongod versions

When using the 3.2.0 RC4 shell to query against a 2.6 or 3.0 mongod/mongos, the shell always returns the following warning:

$ mongo --quiet localhost:27017/test -eval 'db.test.find();'

Cannot use 'commands' readMode, degrading to 'legacy' mode

I would suggest that this error should be suppressed when running in batch mode using --quiet, as it will disrupt scripts that depend on generating output in a certain shape (e.g. XML or JSON). It's less important when running in interactive mode.