Summary:
Tudor who wrote this left the company... so RB.. you are the reviewers :)

1. make default commands as constants
2. remove fake message about ",h"
3. align quota usage from mix to '
4. add support for version command
5. add function to identify built-in command (is needed for an external application to make a decision if something is mandatory or not)

Reviewed By: marcinpe

Differential Revision: D7048169

fbshipit-source-id: b48cf7df28cfa387e028a1cc869332407314c906