done/fail fn can be called 2 times

If a callback function is added (with done or fail fn) between the status change and the call of resolve/reject fonction (like between https://github.com/warpdesign/Standalone-Deferred/blob/master/js/deferred.js#L205-L208 ), then the callback will be called 2 times.

Need to implement a callback stack with disable and lock features, like in $.Callbacks.
