Feature/package version

When I try this on another puppet module:

```
Error: Could not update: Execution of '/bin/rpm -U --oldpackage /tmp/riemann-0.2.0-1.noarch.rpm' returned 1:    package
riemann-0.2.0-1.noarch is already installed

Error: /Stage[main]/Riemann::Package/Package[riemann]/ensure: change from 0.2.0-1 to 0.2.0 failed: Could not update: Exe
cution of '/bin/rpm -U --oldpackage /tmp/riemann-0.2.0-1.noarch.rpm' returned 1:        package riemann-0.2.0-1.noarch i
s already installed
```

for code:

``` puppet
    $package_version = $version ? {
      ''      => 'installed',
      undef   => 'installed',
      default => $version,
    }
    package { 'riemann':
      ensure   => $package_version,
      source   => "/tmp/$package_name",
      provider => $package_provider,
      require  => Wget::Fetch['download_riemann'],
    }
```

Is this a problem with puppet or am I doing something wrong?