Shopify/twine — pull request #19 by maartenvg (2014-12-11 18:41:40+00:00)
Title: Let unbind handle undefined node

### Problem
In a very dynamic situation it might be possible to call unbind on an node that is already deleted. In that case the `node` parameter is `undefined` and should be ignored instead of exploding.

### Solution
Return if node is not defined. Also added some missing tests for unbind.

@pushrax @qq99 @celsodantas
/cc @DrewMartin