You can clone with
It looks like three lines (including a comment) can be removed from the main coffee-script file, as they are only there to support node 2.x. https://github.com/jashkenas/coffee-script/blob/master/src/coffee-script.coffee#L23
If you search this page for registerExtension you can see where it got removed: http://nodejs.org/changelog.html
BTW people are too often using the register.extensions support in production or in npm modules, by requiring .coffee files directly, instead of requiring the .js files generated by CoffeeScript. The coffee-script documentation doesn't encourage it. In fact it encourages the opposite. Perhaps a warning that the quality of error messages will be reduced should be added, though.
Fixes #2441: Remove (deprecated) registerExtension support.