(PUP-3618) Include pkgng provider for FreeBSD

To improve the default state of Puppet on FreeBSD systems, !his work
moves the pkgng provider into core.  Previously, users of the provider
would need to install from the forge module zleslie/pkgng.
Oh, right.  How should this be handled then?  Is there a target version of Facter I should also look to submit the facts into?  I wasn't thinking about that.  This work is stored in a module xaque208/puppet-pkgng currently.