Bugfix for CentOS x86_64 box not having RedHat_64 as type; this will cause a build failure.
Import box templates for CentOS 5.9 and CentOS 6.4.
Merge pull request #36 from juliandunn/rebuild-bento-boxes

Added defs for CentOS 5.9 and 6.4 boxes. Bugfix CentOS 5.8 x86_64 box.