exit on process error
From the iojs docs:
> An unhandled exception means your application - and by extension io.js itself -
> is in an undefined state. Blindly resuming means anything could happen.
>
> Think of resuming as pulling the power cord when you are upgrading your system.
> Nine out of ten times nothing happens - but the 10th time, your system is bust.
>
> uncaughtException should be used to perform synchronous cleanup before shutting
> down the process. It is not safe to resume normal operation after
> uncaughtException. If you do use it, restart your application after every
> unhandled exception!