Allow turning off friendly error pages when running standalone

I'm not sure if I missed something in the docs, but I couldn't find a way to start passenger standalone with the friendly error pages turned off. I added a command line option ```--no-friendly-error-pages``` to allow you to make sure the friendly error pages don't get served in production. The default is still to serve them and they're only off if the new option is passed.

If there is a better way of turning them off in production I'd be curious to know what I missed.

Thanks!