version pinning, support filters with ensure set to absent

This adds support for being able to specify a specific version of repose to have installed at all times.  

```
repose::valve { ensure => '6.1.1.1' }
```

Also added in support for being able to remove filter configuration files without having to specify any other parameters except a title and ensure.  Previously they used to require whatever required parameters that were needed if you were actually configuring the filter.

```
repose::filter::dist_datastore { 'default':
  ensure => absent
}
```