[FIXED JENKINS-20204] Keep up with the new security requirements with Java7u51.

Reference: http://docs.oracle.com/javase/8/docs/technotes/guides/jweb/security/manifest.html
Reference: http://docs.oracle.com/javase/8/docs/technotes/guides/jweb/security/mixed_code.html
Wrote this little diagnostic tool.

Keeping it just in case I come back to this in the future.