Raise exception on missing augeasproviders_core

People who manage their code with r10k have to resolve dependencies by
hand (or using a generator), as such we now helpfully raise an exception
when miaugeasproviders_core is missing.

Author: igalic

lib/puppet/provider/pg_hba/augeas.rb

@@ -1,5 +1,6 @@
 # Alternative Augeas-based provider for pg_hba type
 
+raise("Missing augeasproviders_core dependency") if Puppet::Type.type(:augeasprovider).nil?
 Puppet::Type.type(:pg_hba).provide(:augeas, :parent => Puppet::Type.type(:augeasprovider).provider(:default)) do
   desc "Uses Augeas API to update pg_hba settings"