Restart nginx on significant config changes

When nginx ports or listen configuration changes, server needs to be
restarted and not just reloaded. Since there's no useful indicator when
this should happen, nginx will be restarted when status of symlinks in
/etc/nginx/sites-enabled/ will change (symlinks are added or removed),
config modification will still result in reload only.
Merge pull request #7 from drybjed/nginx-restart

Restart nginx on significant config changes