Support Phusion Passenger

The default Kraken app doesn't work in [the Phusion Passenger application server](https://www.phusionpassenger.com). That's because index.js checks for 'module.parent'. Due to the way Phusion Passenger is implemented, 'module.parent' is not undefined.

This pull request adds support for Phusion Passenger by adding another check. This change has already been accepted by another Javascript framework, CompoundJS, which had a similar problem. [See the discussion here.](https://groups.google.com/forum/?fromgroups#!topic/compoundjs/4txxkNtROQg)

The mechanism used in this pull request is [documented here](https://github.com/phusion/passenger/blob/cae6c0df74d6c6ad08c8960f5735c6f6cb2a72cc/CHANGELOG#L403-L415).