moment/moment-timezone — pull request #31 by Raynos (2013-08-30 21:25:46+00:00)
Title: if moment-timezone has already been loaded then don't do anything

It's possible to have multiple copies of `moment-timezone` in your NPM tree and thus have different copies of `moment-timezone` clobber each other.

This means that `moment.tz.add()` doesn't do what you want as it only adds the things to the current `tz` property of `moment` and not the latest copy of `tz`.