0.4.0: Add support for a global default site

* If `nginx_passenger.catch_default` is set to true, a server entry will be
  set up to return 404 for all requests that a) do not contain a hostname or
  b) contain an invalid hostname. This keeps spiders working by IP address
  from happening across valid sites.
* By default, `catch_default` is turned off
Merge remote-tracking branch 'upstream/master' into generateCertificates