zevarito/mixpanel — pull request #83 by dweinand (2013-03-25 20:27:44+00:00)
Title: Add append_register_once to Mixpanel::Person

Added support for [register_once](https://mixpanel.com/docs/integration-libraries/javascript-full-api#register_once) via the middleware.

This lets you specify a super property that won't be overwritten if it's already set.