Console safe mode

Using the mongo console is scary - it's possible to accidentally issue deletes, updates, and drops. Less scary, but annoying, it's also possible to accidentally create a new collection and think you've, say, added an index on collection A when you created and indexed collection B. Although this can be solved to some extent with user permissions, it would be much easier operationally if the console just took a command line arg that prevented any of these mutations or at least required confirmation before doing so.