ES6: Updated the default parameters test

Added the following checks:
* Explicitly passing undefined defers to the default
* Later defaults may reference values of earlier parameters

This doesn't add the following "pedantic" checks:
* Earlier defaults may not reference values of later parameters
* Defaults may use the arguments object.
* Defaults affect the function length property.
Merge pull request #191 from webbedspace/defaultparam

Updated the default parameters test