Added a check for CVE-2013-4413
* Added a check for CVE-2013-4489
* Added a not_affected attribute to dependency check to flag as not vulnerable
  previous versions

Gem version comparison **must be** refactored... the way it is
implemented is far from being elegant, readable and easy to maintain.
* Added a check for CVE-2013-5671
* Added a check for CVE-2013-4593
* Added a check for CVE-2013-0262