Add check for overwriting existing/core functions

[DinisCruz]

As per this comment http://stackoverflow.com/questions/27291990/better-way-to-implement-in-javascript-after-after-last-before-and-before-last#comment43051894_27291990

Here is a potential solution: https://gist.github.com/P-Seebauer/904b66d4ef9fca51d207#file-gistfile1-coffee

While looking at this, keep an eye for an solution for Add node-webkit support

[DinisCruz]

Here is some more info: http://stackoverflow.com/questions/11587231/coffeescript-getter-setter-in-object-initializers