Fix for issue 185.  This will recompile the catalog when a different :hiera_config value is detected (much the same as is done when different facter facts are used).  When this condition is detected, Puppet's internally cached instande of Hiera is also cleared so that the catalog can be recompiled agsint the differently configured Hiera.
Merge remote-tracking branch 'krancour/issue-185-fix'