puppet-git: added 2013 to copyright notice
puppet-git: added pg_install_required_packages method

Added a pg_install_required_packages method which will automatically
install git and puppet if either one is missing on the target system.

It assumes that the underlying distribution is either a recent release
of Debian (6 and up) or Ubuntu (12.04 and up).
puppet-git: cosmethic change: added a trailing hash sign to header