Add checks for CVE-2013-0155 and CVE-2013-0156

Added checks for latest CVEs. Checks for workarounds for [CVE-2013-0156](https://groups.google.com/d/topic/rubyonrails-security/61bkgvnSGTQ/discussion) like disabling XML parsing or disabling symbol/yaml types.

Also checks for YAML parsing being turned on in Rails 2.x.

Basic version check for [CVE-2013-0155](https://groups.google.com/d/topic/rubyonrails-security/c7jT-EeN9eI/discussion).