[FIX] imageForResource: doesn't exists on 10.6.
[FIX] Verify GPGPreferences' bundle signature and abort to load if verification fails.

- Use SecStaticCodeCheckValidityWithErrors with kSecCSDefaultFlags flags,
  so that the verification makes sure that bundle contents have not changed,
  the main executable has not been tampered with and if other code within
  the bundle has also not been modified.
Allow unsigned Code.
Code sign check
Version 1.0.1