Add support for Passenger 4.x.x

Use `PassengerEnabled` instead of `RailsAutoDetect` for passenger 4.x.x

Tested with:
- Ubuntu LTS 12.04
- Ruby 2.0.0-p247 (installed with ruby-build)
- Passenger 4.0.14

```puppet
class { 'passenger':
  passenger_version      => 4.0.14,
  passenger_ruby         => '/usr/bin/ruby',
  gem_path               => "/usr/lib/ruby/gems/2.0.0/gems",
  gem_binary_path        => '/usr/bin',
  mod_passenger_location => "/usr/lib/ruby/gems/2.0.0/gems/passenger-4.0.14/buildout/apache2/mod_passenger.so",
  passenger_provider     => 'gem',
  passenger_package      => 'passenger',
}

```