What's the advantage of this over pgdg-centos91-9.1-4.noarch.rpm? I think something like

```ruby
package_from_url 'http://yum.postgresql.org/9.1/redhat/rhel-6-x86_64/pgdg-centos91-9.1-4.noarch.rpm'
```

can replace the above `cookbook_file` and `template`.