Only call iterator functions with context if provided
Remove argument reasignment to promote engine optimization
https://github.com/petkaantonov/bluebird/wiki/Optimization-killers#3-managing-arguments
add history
Merge branch 'createCallback' of github.com:megawac/fast.js into 3-iter-funcs-context
prove #3 is faster
Merge pull request #11 from codemix/3-iter-funcs-context

Iterate function context