Source maps in node

Addressing https://github.com/jashkenas/coffee-script/issues/2787
Ported stack trace [patch](https://github.com/michaelficarra/CoffeeScriptRedux/blob/master/src/run.coffee) from Redux.
passed `cake test` on node v0.8.17

This enables source mapping in `exports.run` by default, I would like to know your opinion.
Anybody think it's appropriate?