Currently if we try to run mongorestore to restore v2.2/2.4 users to MongoDB 2.6, it will fail with:
assertion: 17415 Cannot restore users with schema version 1 to a system with server version 2.5.4 or greater
It would be nice if mongorestore can restore and upgrade v2.2/2.4 users to MongoDB 2.6, or if there is a script/tool we can use to upgrade the user schema.