argument Object Optimizations

Related to #2148 

Source was [this](https://github.com/petkaantonov/bluebird/wiki/Optimization-killers#3-managing-arguments)

Skipped "methods.js"
Changes per [this](https://github.com/petkaantonov/bluebird/wiki/Optimization-killers#31-reassigning-a-defined-parameter-while-also-mentioning-arguments-in-the-body-typical-example)