Fix `child_process.fork` patch

Fixes #2919 by simply leaving `execPath` alone. (Currently `bin/coffee` is called with node's `execOptions`.)

The `coffee` "binary" is now used as the module with the actual `.coffee`-module as its first argument. This also makes the patch work on Windows (the friendly OS where executability is determined by file extension and shebangs don't exist).

Also fixes `.fork` calls without an arguments array. (Currently `options` is set to `[]`)