emberjs/ember.js — pull request #2544 by komasayuki (2013-04-24 06:23:25+00:00)
Title: Fix incrementProperty/decrementProperty to be able to use with 0

Ember.Observable#incrementProperty and decrementProperty can't be able to use with 0.

// person.age = 25
person.incrementProperty('age',0);
// person.age -> 26 , not 25

http://jsfiddle.net/ZCxwH/