As of the release of Puppet 3.0.0, hiera-puppet has been incorporated into the puppet codebase. The standalone hiera-puppet is only needed for releases of Puppet prior to 3.0.0, which are all in bug-fix only mode. The 1.x branch is for those older versions of puppet and is only open for urgent bug-fixes. However, do not submit fixes against this repository.
File bugs for hiera-puppet against puppet itself and submit patches as pull requests against puppet as well. If it is an urgent bug that is in hiera-puppet 1, then let us know and we will port the change over.