Add jshint to `npm test` to keep code clean.

Added two jshint annotations to allow `== null` in the places where we
explicitly want to test against null and undefined.
isArguments method
Merge pull request #214 from cscott/jshint

Add jshint to `npm test` to keep code clean.
Merge pull request #216 from ljharb/is_arguments

Adding an isArguments method.