• Add Rubinius 2.2.6
• Avoid sed with extended regexp for cross-platform compatibility
• Update to yaml 0.1.6 for CVE-2014-2525
• Add rbenv install --skip-existing <VERSION> option
• Avoid re-downloading if there's a valid tarball in build location
• Fix re-downloading tarball when destination file already exists
• Improve check for user-specified build definition